Feb 5, 2019

Adventure Games: What I Meant When I Coined the Term

I coined using the term "adventure game" for roleplaying games in February 2012, and I've been using it since then consistently instead of "roleplaying game". There's been a recent discussion around the term started by Ben Milton, so I thought I might as well explain why I started using it in the first place.

I've summarised bits and pieces of my philosophy before on my blog. One doesn't have to read all of these, but they show variations and developments in my thought over the past seven years.

The Long Narrative
Roleplaying: Beyond Talking
The Basis of the Game Is Making Decisions
Running Technical Plots
Layers of the Sandbox
Low Concept Campaigns
Crappy Plotting

 I would say I first began thinking along these lines in 2008, when 4th edition Dungeons and Dragons came out and there was a sprawling online kerfuffle over "dissociated mechanics" at the same time as a concept known as "bleed" began to sweep LARPing circles. There was also a lot of debate around how "collaborative world building" and "collaborative storytelling" could be used to help referees give up the idea that they were writing an epic fantasy novel with the players as the railroaded protagonists. I don't know how successful this actually was (I still see questions regularly on Reddit about how to get the players to follow the amazing story the referee has come up with), but it was the context around when I began to think about what I used to call "anti-narrativism".

Anyhow, the four years from 2008-2012 not only had me reading a lot about these controversies, but it also saw the end of my then-regular gaming group (in late 2009, when the referee moved out of town) and my first foray into OSR-style games (Swords and Wizardry Complete, in particular). I engaged in a process of reflection about what I was trying to do with and in "roleplaying games" as I still mostly referred to them at the time.

The answer to what I concluded isn't simple or easy to sum up, but one element was that I realised that my prior conception of "roleplaying games" was not that different from the "immersion" crowd, and while not wrong, it was simply insufficiently broad to encompass all the things I liked about games, and also, from the perspective of producing enjoyable games, it misled me about how to do that by encouraging an emphasis on dramatic elements like acting out characters and vividly narrating a story.

Instead of skill of the portrayal of the character, it was the agency (and on the level of the party and group, the deliberation that fed into that agency) that I particularly prized as a player, and that I realised formed a set of key skills that players needed to develop even before they built up their acting chops.

To provide the stable and intelligible foundation for the shared world the player-characters move through, I needed to structure the decisions and consequences of those decisions, and to constantly communicate them clearly back to the players.

A player might talk in the third-person about their character or not, they might use a funny voice or not, their character might not have any family or background or whatever, but if we could make the choices that character made interesting and evocative and varied and relevant, the rest fell into place.

I chose "adventure game" to represent that refocusing (I also chose to begin referring to the "dungeon master" or "games master" as a "referee" most of the time). For me, the core of gameplay is not narrative (not a series of rising actions that develop to a climax and then resolve in a denouement), but iterative, and the things being iterated and reiterated are procedures, little list of instructions that govern how and when to apply or not apply the various rules.

The classic example in most adventure games is the combat procedure, which tells you how to set up combat encounters, determine in what order players proceed, how and what they can do, and then delivers some set of consequences based on their decisions and various randomising factors. Once you complete a loop of this procedure, you reiterate it for the next combat round until some end condition is met.

My preference is to be continuously enacting one procedure or another, or when not possible, to provide a set of structured steps that lead the players through deliberations with one another that resolve into decisions they make and consequences they bear for them. Oddly, this often ends up resembling a traditional story (and I have no objection to its mere appearance as such), but I treasure the times where it doesn't in particular, as these are the moments where the adventure game medium generates something new and unexpected.

The "adventure" then is not the narrative the player-characters flow through towards an inevitable climax and resolution, but the procession of problems, challenges, etc. they face; the decisions and deliberations they make about what to do about each problem or challenge; and the procedures they enact as part of those decisions, and the consequences of all the above interacting with one another.

Many people have been calling this sort of playstyle "OSR-style", though that to me associates it too closely with a particular subset of games (mostly rules-light D&D variants) and subculture of product design, and loses the idea that it is a playstyle that can be applied to almost any "roleplaying game" (Some with more easily than others, admittedly).

Recently, as people have begun wanting to move away from calling themselves "OSR" for political reasons and to characterise their playstyle using a different term, I've repeatedly suggested "adventure games" as an alternative. I think of the OSR as a particular subculture, with a particular attitude towards independent publishing, the history of gaming, etc., but I think the playstyle characterised by "adventure games" is one that is not specific to it, and that this playstyle should be developed and shared more widely so that even people who are not part of that subculture can learn it and adopt whatever practices from it they find most useful, in the same way people think of "storygaming" or "trad roleplaying games" as distinct playstyles to be developed and studied.

In that sense, I don't see "adventure game" as a replacement for the "OSR" concept itself (referring to the subculture), but only for the "OSR-style" or "OSR playstyle" terms. And obviously, I encourage you to use it as such.

Jan 30, 2019

Building my Own Referee Screen

I'm building myself a new referee screen out of four 11 x 14" mounted artist panels (pre-gessoed) that are being bolted together with hinges and held together by magnetic tape. The large size and the hinges mean that it'll fold up into two boxes each with an internal cavity big enough to hold 8 1/2 x 11" pages without folding. The outer surface will be covered with chalkboard paint so I can write on it easily (using erasable chalk markers).

Here's a work-in-progress photo from last night, after the main panels had been painted (I did the sides after taking this photo). It took about four coats of the chalkboard paint (I used the Rustoleum one) to get a nice thick coating, and it'll take three days to fully cure. I'm going smooth it out with a fine-grain sandpaper on Friday, check if I need to reapply another coat anywhere, and season the chalkboard paint (You rub chalk all over it to block up some of the pores in the paint) if it's totally cured.

Really looking forward to trying this out at the table. Depending on how it works, I might try a second version using the rest of the paint and magnets that's made of unmounted wooden panels with glass cabinet hinges (no-screw clamping hinges) holding it together. Wish me luck!

Jan 29, 2019

Combat Style Traits in Mythras

If it's never come up, I'm not a huge fan of the default combat style traits in Mythras, since the effect of most of them is to make you ignore a cap on your combat style in some situation. e.g. When you're riding a horse in combat, your Ride skill "caps" (determines the maximum percentile value of) your combat style - unless you have Mounted Combat, in which case you get to use your full combat style.

Rules-as-written, a combat style trait only grants one benefit, and you can only have one trait per combat style, but this seems to be something honoured in its breach in fan-made material (Shout out to the Notes on Pavis guy for running a great blog). My assumption is that this represents running up against the limits of how this works in actual play, since it's something I've run into as well.

To recap the situation with combat styles in Mythras: The average Mythras character has 1 or 2 combat styles to start, and perhaps learns 3-4 total over the course of a long career. These combat styles form the primary skills characters use in combat for both attack and defense, and thus are a priority for most characters to boost. Those 1-2 additional combat styles will primarily be driven by either the traits of a new combat style, or the need to shift the weapons they use (or some combination of these two).

With the typical split between combat and non-combat characters in the parties I've seen (about half of all characters being combat-focused, meaning they get two styles), assume a starting party has about 1.5 combat styles per party member, except these aren't unique styles - most characters have a single cultural style common to all of members of that culture, and most Mythras parties are from a common cultural background. So only the 0.5 extra combat styles per PC are actually unusual or unique ones. In a party of four characters of shared background, that means you'll have one common style, and two unusual ones, each accessed by only a single PC.

How many combat styles there are in a particular setting varies widely, but typically you have between 3-6 per culture, depending a lot on military specialisations available within that culture. Most Mythras settings only use a small subset of the giant list of weapons included in the Mythras corebook - between 6-10 is typical, with 3-4 weapons per combat style, and in practice, you see a lot of repetition of the best weapons in different styles (Hello shortspear my old friend).

What this means in practice is that a lot of the odder combat style traits tend not to appear - they're either not attached to the main 3-6 options available, or they're just not present among the 3 different combat styles in a 4-person party (if you run with six PCs, you'll end up with 4 different combat styles on average). Also, some of the traits are far better than others because the combat situations they apply to are far more common, and these traits tend to be the most common, repeating across combat styles.

One of the outcomes of all of this is that combat style traits are not actually a very good method to ensure PC combat styles aren't capped. I'd rather just not have the caps in the first place, since they tend to take exciting action combats where the PCs are doing things like chasing people around on horses or climbing the rigging of a ship or storming a castle's walls and turn them into frustrating whiff-fests. Realism be damned, this is a game where you can play a cat-man wizard, and that cat-man wizard should be able to stab a guy while swinging from the rafters.

In place of the current combat style traits then, I propose that caps should be abolished in most cases, and combat style traits should not be the mechanism by which they are nullified. Instead, combat traits should focus on empowering characters with options or intensifying their combat advantages.

Here are some proposed new combat style traits. Each one has several abilities it grants to someone trained in a combat style, and most a couple of regular combat style traits cobbled together.

Allows the use of the Flurry special effect so long as the character is wielding two weapons and the extra attack uses the second weapon.
If a character's damage modifier is two steps higher than an opponent's, their weapon size is considered one step larger for the purposes of bypassing parries.
Any psychological resistance rolls by an opponent are one step harder.

May use Evade to dodge attacks in melee combat without going prone.
Allows use of the Flurry special effect so long as all extra attacks are made with a single weapon.
Can use the Change Range action to automatically withdraw from combat without a roll.

Making a mounted charge with this style does not incur the one-step penalty to hit.
A character may spend action points to defend against attacks targeting their mount.
A character's damage modifier counts as one step higher for the purposes of calculating knockback.

Line Infantry
If three or more characters with this trait are in close order with one another, then:
Any enemy who engages them has their action points reduced by one.
They automatically get the benefits of using the Brace action against Knockback, Leap Attacks and Bash attacks.
Each character can ward an additional location using a shield or secondary weapon.

A character may make ranged attacks while running (but not sprinting).
When using a ranged weapon, the hit location of a successful attack may be shifted to an adjacent location.
If three characters with the Marksman trait attack a single target or group of targets in close order, the targets are automatically Pinned Down (per the special effect).

Mounted Archer
A character may make ranged attacks while their mount is running (but not galloping).
When using a ranged weapon, the hit location of a successful attack may be shifted to an adjacent location.
A character can evade attacks without going prone while mounted, using their Ride skill in place of Evade.

Can use the Change Range action to automatically withdraw from combat without a roll.
A character increase the size of your weapon by one step while parrying so long as they don't attack that round.
Outmaneuver rolls are one step easier.

Can use the Kill Silently special effect.
When using a ranged weapon, the hit location of a successful attack may be shifted to an adjacent location.
Opponent's rolls to outmaneuver an attacker using a combat style with Stalker are one step harder.

Can use Grip as a defensive special effect
Opponent's rolls to evade, break free of, or resist immobilisation in a grapple are one step harder.
Unarmed blocks and parries count as "medium" sized.

Because the average character has only 1-2 combat styles, adding a couple of extra conditions or abilities onto each combat style trait doesn't increase the complexity very much for any given player. Monsters and most opponents don't even have combat style traits, so while the occasional custom-built major villain will have a touch more complexity due to this, most opponents won't be any harder to run for the referee.

You can make combat style traits that require 3 or more characters to get their full benefits available as cultural styles, so that most of the party will end up with them.

If you don't want to get rid of caps, then I would suggest at the very least combining a no-cap combat style trait with at least one other combat style trait that does something interesting.

I haven't play-tested these yet, but I'm hoping to later this year when I start up a Dawnlands campaign.

Jan 14, 2019

The Basis of the Game is Making Decisions

Some people are going to find what I'm talking about in this post so obvious they won't understand why I feel the need to mention it. To those people, I offer my apologies, but I have realised from discussion with a broad spectrum of roleplayers over the years that it is not so obvious as it seems.

The core activity of roleplaying games is making decisions. Every other activity feeds back into this core in one way or another. Rules are there to control and shape the field of possible decisions, determine the likelihood of particular outcomes of those decisions, and to structure who makes which decision. Characterisation, party dynamics and the world exist to shape the style of decision-making and the values and tools brought to it; to establish decision procedures; and to provide stakes and consequences for decisions.

I would contrast this understanding with the one that superficially claims that a roleplaying game is like a television show, novel or movie that is focused on telling a captivating narrative for an audience. This kind of understanding, taken to its extreme limit, leads to railroading, which I understand as the negation of player characters' ability to make meaningful decisions, combined with the players' knowledge that this is the case.

I think a decision-based understanding of gameplay is superior to this narrative understanding for two reasons. The first reason is paedogogical, and the second is schematic.

When explaining to a new player or potential player what the game is and how it is played, people often repeat some line like "You're like the star of a TV show going on an adventure" or "You're a character in a fictional world who lives out a story". This implies that the most important activity or skill is acting, and the structure of play will follow the scene-framing and development of other narratives. It is therefore, a rude shock when they start playing a game and they are not very good at acting out their character and the flow of a session does not follow the narrative progression of other media.

This shock is now sometimes called the "Matt Mercer effect" after players who got into D&D from watching Critical Role, but who are displeased to find out that they can't plunge immediately into a complicated and immersive narrative. I don't blame these people for this shock. They were led to believe one thing, and rudely surprised when it turns out that belief was just propaganda. On top of that, they don't necessarily know how to improve the situation they find themselves in and move to the sort of immersive game they were lured in with - witness the endless threads on Reddit and rpg.net and other forums on this very topic.

Paedogogically, I think focusing on decision-making instead is probably more useful for that new player. The new player begins by making and justifying decisions with the character as a pawn (on the character's behalf), then learns how to make decisions based on the character's subjectivity (as the character). Similarly, they learn to justify their decisions to the referee or other PCs on behalf of their character (or out of character), and then how to justify them as the character to the other character in world.

They're not rigidly locked into any one of these four options, of course, and further learning would be how and when to deploy each. This helps new players to feel like they're increasing their agency over time, rather than constantly failing. In my experience, this is both an easier course of development for new players to grasp, as well as being more likely to retain them as players than frustration and failure are.

Schematically, I've written about this before in my long post on "anti-narrativism" in constructing D&D stories. A distillation of the basic point is: Rather than structuring the progression of a campaign as a series of dramatic scenes with the PCs flowing from one to the other, I think games should be structured as a set of situations where PCs must make decisions. The occasional montage or descriptive flourish isn't awful, but thinking of the development of the story in terms of decisions actually provides a clearer and more effective plan than trying to think of the next "chapter".

As a bonus, the superficial sensual effect of a decision-based structure is that it actually seems more like a traditional narrative than trying to plot out a story as if it were a novel, television show, or movie, because making decisions and dealing with the consequences of them is what happens to characters in a well-written story.

I think many people will claim that they already accommodate the idea of decision-based adventure gaming in their planning, and I'm sure many do, but I am 100% certain that there are many more people who could improve their games by shifting their mindset over to this, or increasing its prominence and salience within the mix of ideas they have about planning. I especially encourage new players and new referees who are having trouble creating the kind of richly immersive world and story they admire in other people's games to try adopting this mindset.

Jan 3, 2019

Improving Descriptions Using the Gricean Maxims

I rarely make absolute statements rather than propositions or suggestions, but I can't think of a countervailing example to the statement that good descriptions improve roleplaying games. That is, the better the descriptive powers of the referee and players, the better the game. I don't necessarily mean complex, verbose descriptions (some people like them, some people don't), nor do I idolise the modern imitators of Hemingwayesque concision.

Rather, I want to talk at the level below that aesthetic level, at the level of the cooperative principle and its derivations, the Gricean maxims. For people who've never heard of them, here's a brief explanation in text, and one in video. The basic idea is that Gricean maxims are the principles that an audience uses to evaluate a speaker's utterances in a cooperative exchange. One can not only apply them, but also flout them (and opt-out of them under certain circumstances, and just straight up lie, of course).

The Gricean maxims are the root understanding behind the old roleplaying joke where a referee describes a throw-away NPC and the mere act of describing them causes the players to want to interact with them or suspect them of being involved in the plot somehow: the joke is just that they incorrectly apply the maxim of relation beyond a reasonable level.

Anyhow, weird as it may be to say about something this basic, I'm amazed at the number of games I've played in where the referee flouted or failed to wield the Gricean maxims fluidly when describing the world to the players.

Sometimes this is because they don't frame the utterances well. They fail to establish that this bit of scene-setting is just a bit of evocative description like an establishing shot in a movie, there to create a picture in the players' heads, instead of a sequence they're expected to execute decisions in relation to. (Secret bonus referee tip: I tend to gesture more dramatically than usual while doing these so that people understand I'm just describing things)

Sometimes this is just because they describe a ton of irrelevant crap in a manner that disguises instead of distinguishing what is relevant. Sometimes it's because they withhold essential information, often because they mistakenly think they're in a competitive exchange: Waiting for the PCs to ask about it or to figure out that they need to use a skill or power to discover it.

Sometimes this is because they're working from a module that was written by someone who didn't follow the Gricean maxims in its composition, or that was just otherwise written in an unclear way that buries the relevant, truthful information the players need in a place where it can't be easily reviewed.

All of those are bad situations to be in, both as a player and as a referee. They could all be improved by following the Gricean maxims. In fact, if you robotically follow the Gricean maxims for any situation the players are in, while merely speaking concisely and using prosaic terminology, you'd be surprised at how players will compliment your descriptive powers (I know this because I do it all the time). Add in the occasional evocative or captivating flourish, and they'll rave.

Individual referees have their own unique styles, and the members of any given group will be happier or not with a given referee's style. I don't think aesthetics are purely arbitrary and individual, but I also don't think it's worth trying to denounce or bolster a particular aesthetic style or taste outside of a concrete instance. But with the Gricean maxims, we are sub-taste, at the level of the pragmatics of speech and conversation, and mastering the pragmatics will only improve things for everyone involved. 

Dec 20, 2018

Organising the Senses in Mythras Sorcery

Mythras sorcery has a number of spells - Mystic Sense, Phantom Sense, Perceive (Sense Type), Project Sense - which are broken down into individual spells by which sense they affect. Only Phantom Sense explicitly lists the folk taxonomy of five senses and how each can be altered by the spell, but I think the default assumption for all of them except Perceive (Sense Type) is that the folk taxonomy is fine, and Perceive mainly involves augmenting the existing senses, so that one can e.g. see infrared or smell fear and the like.

I, along with modern science, think the folk taxonomy of five senses leaves out a lot of actual senses that humans have, let alone weird creatures that might exist in a fantasy setting. I thought it might be worth reorganising and categorising senses that sorcerers can affect with a single spell. Such a catalogue would hopefully help spur the imagination and make some of the selections more desirable than relying on the folk taxonomy alone would.

Here's that catalogue, along with the explanations for each. Each line is a single sense-type for spell purposes.

Sense Types
Electroception & Magnetoreception
Sight (Visual, Infrared, Thermovision, Ultraviolet, X-rays) & Chronoception
Sound & Echolocation
Smell, Taste, & Chemoreception (Flavour)
Touch, Proprioception, Nociception, Balance, Mechanoception, & Thermoception (Feeling)

Electroception and magnetoception are the abilities to sense electro-magnetic fields. The difference in the two tends to be whether it involves active pulses (most electroception) or not (magnetoception). These senses are especially common in insects, birds and fish, and extremely useful for navigation (humans use compasses to similar ends). This is an unusual set of sensory modes, but I could see it being kind of cool for Mystic Sense in particular - you feel yourself in a rippling field of magical energy that conveys information through prickling feelings. Scientifically sophisticated sorcerers could do all sorts of interesting things with the ability to sense and measure paramagnetism, diamagnetism, ferrimagnetism, antiferro- and antiferrimagnetism etc.

Sight's domain is obvious, but I do think it should explicitly cover sight beyond the ordinary visual spectrum. I'd include chronoception (the sensation of the passage of time) with it not because they're tightly linked (they're not) but because I think the most obvious way to mess with, fool, or manifest altered chronoception involves vision. If suddenly everything you can see is moving in a blur, or like molasses, your chronoception is going to fool you.

Sound and echolocation are similar to electroception and magnetoception in that one is a passive sensation and the other involves actively pulses which are received and processed. I think this is a fairly obvious combination of senses. I would allow Phantom Sound to produce fake speech, something that's not explicit in the spell description but that extends its usefulness while not cleanly being covered by another spell.

Smell, taste and chemoception are all variations on the same sensory mode, coming in through different organs. I would let Phantom Smell /  Taste / Chemoception include faking the effects of poisons and other drugs, albeit these effects would be illusions. Great for psychedelic purposes or for making someone feel like they've been cured of an ailment. I would also allow the Phantom version of this spell to trigger allergies. Taste on its own is one of the weaker and less useful sense types to associate with a spell, so combining it with smell boosts the desirability of taking it. For shorthand, I'd call it "Flavour", a word that (at least in my dialect of English) refers to both smell and taste.

Touch, again, has an obvious domain. Proprioception is being able to feel the movement of your body, including locating where your limbs are (Octopi, oddly, lack this sense and use visual cues). Nociception is feeling pain. Thermoception is feeling heat and cold, though strangely, it's a separate sense from feeling burnt (which uses nociceptors) which is why you can feel like your mouth is one fire from eating a chili without being confused about the actual temperature your mouth is. Mechanoception is feeling and interpreting vibrations in the medium around you (with its finest and most powerful expression being the Earth Sense ability on page 215 of Mythras). Balance (and feeling the force of gravity more generally) is distinct from proprioception. I will admit to a slight inconsistency here, in that smell, taste and chemoception are related senses performed by different organs, while this collection of senses is mainly the range of senses performed by a single organ (the skin), combined with proprioception and balance. I think English, which uses the verb "to feel" to cover all of these, provides a verbal-conceptual nexus by which players can get a handle on the collection. In fact, to avoid having such a large list, I would recommend calling this "Feeling" for labelling purposes - Phantom Feeling, Mystic Feeling, Project Feeling, etc.

Thaumoception would be the ability to detect magic. This is already a sensory mode some monsters have in Mythras (using the "Magic Sense" ability on Mythras p. 216), and including it as a sense allow one to use Phantum Sense to replicate something like "Nystul's Magic Aura" and other misdirection spells from D&D - hiding the aura of magic, making a non-magical item seem magical, or changing what kind of magic seems to be behind an effect.

Bioception and Thanatoception are the abilities to sense the presence of life and death / undeath respectively, as covered by the abilities "Life Sense" (Mythras, p. 216) and "Death Sense" (Mythras, p. 215) respectively. No real creature has these, but they exist as senses in Mythras, so spells that manipulate them or that allow one to adopt them briefly (Perceive) should be possible. At first I thought these should be expressions of a single underlying sense, but they're mechanicall and thematically distinct enough to make sense as different senses.

Anyhow, I hope this catalogue is useful and encourages players of sorcerers in Mythras to learn or develop spells involve some of the more unusual sensory possibilities. Just to be clear, this isn't the only way of carving these up - many people (e.g. neuroscientists using a categorisation based on nerve-functions) would probably treat thermoception, nociception, chemoception, and proprioception as distinct from touch but integrally related to one another.

Nov 26, 2018

Some Methods for Establishing Prices

For the past few years, I have adapted a technique elaborated by Zak S. in his Vornheim supplement for setting the basic prices of goods. Here, I want to discuss the technique, some expansions and adaptation I've made to it, and some alternative techniques I also deploy to resolve the question of "How much do things cost?" and "Can I get a deal?"

Zak's technique is to calculate the cost of an item as a number of silver pieces (in a silver standard economy) equal to the # of letters used in its name and description. "Rope" costs 4 sp, for example. This runs into a bit of a wonky situation with the way plurals work in English, so I generally ask people to specify quantities (getting ten of something for slightly cheaper than the cost of nine is treated a bulk discount).

The first expansion of this technique I've introduced and experimented with is to modify the cost of the item through the application of negative adjectives. The negative adjectives reduce the value of the item by the # of letters in them. If they would reduce the cost of the item to zero or less, instead reduce the type of currency down one step (so from silver to copper) and then continue subtracting copper pieces based on the remaining unused letters in the negative adjectives. If you bottom out of copper, well good luck, it's trashed.

You can, of course, fix up or repair an item to remove negative adjectives, restoring its value.

The second expansion involves using this to haggle. Each side gets one or two passes at describing the object, trying to tack on adjectives describing its quality, value, etc. to boost or diminish its price. I typically allow three adjectives to be added per pass. Anything they say about the object becomes true, but you can't fundamentally change the object, so no taking this "jade ornament" and saying "It's actually a katana".

I usually make the NPCs go first, partly to give the players an idea of how long a pass is and what kinds of claims you can make about items during one. You should encourage the PCs to write down the specific adjectives they're asserting, and write down your own in turn. The fun of this can evaporate and it can be tedious to track everything after more than two passes on each side, and after four statements of three adjectives each, you have twelve modifiers (Try this: Write the adjectives in matching pairs from each side on grid paper with one letter per square. Cross off letters in each instance until you're left with a subtotal for each side, then subtract the smaller subtotal from the larger to arrive at the actual price difference).

This whole process works well when you're buying or selling individual items, especially if they're high-value treasure like magic items (and you can slide in plot-hooks about them through careful preparation for your descriptions as well).

One minor but important point is that once PCs decide to do this, they are locked into the sale or purchase - no backing out. The assumption is that this represents the best price they're able to get for the item.

For treasure items that don't have a clear value because they're made of precious materials, magical, or whatever, I use this technique to quickly generate their value.

For large bulk purchases or sales of mundane items, like when the PCs are resupplying their mundane gear; equipping a caravan, ship or castle; or engaging in the speculative trading of bulk goods, I just roll (2d6+3) x 10% x list price. That gives you a range between 50% and 150%, with the majority (2/3rds) of all results between 80% and 120%.

I got this trick from Mongoose Traveller, which uses 3d6 x 10% to calculate the sale price of bulk goods. But having played around with it a bit, I think the extremes are a little more extreme than I normally want, except in a game where the PCs are merchant-traders trying to get rich and so those rare purchases at 30% of list price and 180% sales are huge wins for them (that is, when playing Traveller). And conversely, sales at 30% of value and purchases at 180% are really disincentives to get rid of stuff, disincentives that stop the conversion of treasure or goods into cash entirely. A system for pricing that set them so that people don't want to buy and sell is not a good pricing system.

I also only roll the 2d6+3 once per visit to town, instead of doing it for individual transactions or shops. It covers both sales and purchases simultaneously - if you're in a market undergoing inflation, you're also taking advantage of that inflation when you sell things, and vice versa with deflation. This means you only have to do the calculations once (I use an Excel spreadsheet when I have a computer handy) instead of repeatedly.

If PCs are unhappy with market conditions, then I provide them with two options, one of which they can engage with prior to going on the market, and the other they can engage afterwards. First, for specialty treasure, they can use the haggling procedure mentioned above. Second, along their adventures, I try to have them encounter and form relationships with merchants. If they have a special relationship with someone, then they can make a single new roll just covering things they're buying or selling from that merchant, and take the better of the two for their purposes.

I roll the market conditions after the specialty items are dealt with because it speeds things up by removing the comparison between the market prices vs. possible haggled prices prior to decision-making.

e.g. The PCs in one of my Necrocarcerus campaigns once saved a gas station clerk from being transformed into a skeletal warrior by a fire cult / undead rights organisation. This would count as a special relationship that would allow the reroll if they tried to buy gasoline or other supplies from his gas station.

The order of procedures for integrating all of this in my games is as follows:

1) PCs arrive in town and announce they want to buy / sell supplies and treasure.
2) Magical and specialty treasure is handled first. PCs haggle with merchants over the prices and the sales are concluded as described above.
3) Roll (2d6+3) x 10% and calculate prices for mundane and bulk goods.
4) PCs draw up a list of goods they want to sell or buy w/o fuss or muss. The modified prices are applied. If there are specialty items the PCs didn't sell via haggling, they may now sell them as well, at market prices.
4a) PCs may withold some items to sell at special merchants they have relationships with. If so, they may reroll for those merchants and recalculate the prices then make their sales or purchases.