Price changes for merchandise

In the Core ACKS rules, we read

"The market price is the prevailing price for that market, and should only be calculated once for each type of merchandise for each visit to the market."

but a little later we also read

"The market price is calculated once when merchandise is bought, and again when it is sold in a different market. If the adventurers wait in the same market hoping for the price to change, there will be a 10% cumulative chance of a price change (re-roll) for each type of merchandise each month."

These seem inconsistent to me, and don't seem to cover all cases.

Example: A caravan leaves, then returns a couple months later. Which of these is correct?

  1. Recalculate all prices (literally "calculated once for each type... for each visit to the market").
  2. No change in prices (since the adventurers didn't literally "wait in the same market hoping for the price to change").
  3. 10% chance of price change (since it's the first month they're back)
  4. 20% chance of price change (since it's two months total they've been gone)
  5. 10%, then if that fails, 20% chance, sequentially (as though the adventurers had waited and checked during both months)

I think that 5 is the most consistent answer -- since I think that's what happens if they don't move at all, and I don't see how the adventurers traveling should change prices at a different rate. But even here, I'm not sure I'm reading the rules correctly.

Exactly how quickly prices change will have some substantial implications for the profitability of trade -- how long good routes can be exploited, etc.

Also, as long as I'm thinking about trade, how does the experience threshold work for expeditions that don't take an interger number of months, like "45 days"? Is the number of months rounded (up? down?), or is the threshold prorated by days? (The only clue I can find is specific to the magical research rules, which indicate that times below one month should always be rounded up to one... which might indicate that rounding is normal, or might indicate it applied only to research and NOT to trade!)

I would probably prorate here, to avoid the weird "I was one day late so I got no experience" cut-offs.

I take the price change as point 5 (so 10% for the first month then, 10% if it succeeded or 20% if it failed for the second month).  Unless there is some obvious reason to have a deviation (like the market's stone mine being over run by beastmen or other monsters).  Thus the accumulation that at some point prices will change, even if it is some 6-8 months down the track.
The group leaving and returning to the same market would just offer them alternatives to off-load at other markets than just holding onto the goods and going no where for those months.

As to rounding experience, I suspect that is left for a judge to interpret.
For me, for a day or so either side, I typically either round fractional experience in the players favour if they are longer than a month, or against the players favour if they are short of a full month.
If it end's up being more than a few days I divide the monthly earning by whatever part of the month (presuming a 30 day month), for example, for 45 days they would get 1.5 times the xp, for 80 days that would be 2.6 times the xp and so on.

Both of those seem totally reasonable to me, but I've learned to always ask, since sometimes there's an elaborate explanation for why things work a certain way that I would never have figured out myself.

It's #1. You could use #5 if you'd like without issue.

The economic system is a mix of rules that are simulationist with some rules that are what we might call "straight jackets" against exploitative player behavior. 

In the first draft of the rules (in my own campaign), the prices changed each time the adventurers visited the market. The adventurers would therefore enter the market...leave...enter...leave.... each day until the price was what they wanted. This is similar to a videogamer hitting "save game and load game".

Therefore, I added a rule that said the price is calculated once when you visit to buy merchandise, and then again when it is sold in a different market. This encouraged the adventurers to buy whatever the best-priced goods were and head off on their mercantile expedition.

But this created some lack of realism. While leaving and entering the market each day hoping for huge price changes was unrealistic, certainly the market price could change given enough time. So I added the rule about prices changing randomly after a month, two months, etc.

One could carry this to the next logical step (your interpretation #5) and gain additional realism. But it adds more paperwork as you have to track historical prices for each market they've visited, date of last visit, and roll for price changes.

So, base system is as follows:

  • Adventurers visit Market A. Good X is priced at P1. Adventurers buy X at price P1.
  • Adventurers go to Market B. Good X is priced at P2. Adventurers sell X at price P2.
  • Adventurers return to Market A. The price of X is now recalculated to P3.

Let's assume they don't like P3 and hang out.

  • Adventurers are at Market A. Good X is priced at P3. Adventurers linger one month.
  • 10% chance of P3 changing. Roll is 24, it doesn't change. Adventurers linger another month.
  • 20% chance of P3 changing. Roll is 81, it doesn't change. Adventurers linger another month.
  • 30% chance of P3 changing. Roll is 07, it changes to P4. Adventurers buy X at price P4.

So you can see that the Judge only needs to worry about the prices of whatever market the PCs are currently at, whereas the more realistic system #5 would require historical tracking:

  • Adventurers visit Market A. Good X is priced at P1. Adventurers buy X at price P1.
  • Adventurers go to Market B. Good X is priced at P2. Adventurers sell X at price P2.
  • Adventurers return to Market A. Judge calculates length of time since adventurers visited A. It has been three months. Judge rolls against a 10%, 20%, and 30% chance of price change. If price changes, Judge recalculates it.



No, I see the reasoning here. I think historical tracking would work reasonably well for either of our current campaigns, which have only a few locations with large enough markets to make trade appealing. At the same time, I'm worried that it locks the prices down for so long that a single short trade route could be used dozens of times to make unrealistic profits.

The advantage to changing prices more quickly is that it takes care of the "prices should really adjust toward one another as the adventurers ran a caravan every week" problem -- which is especially true for smaller markets that should have very limited supply and demand.

It is a little weird that adventurers can keep prices from changing nearly as quickly by just sitting around, but that does partially implement the "no trade keeps demand from being met" corollary of the above.