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?
- Recalculate all prices (literally "calculated once for each type... for each visit to the market").
- No change in prices (since the adventurers didn't literally "wait in the same market hoping for the price to change").
- 10% chance of price change (since it's the first month they're back)
- 20% chance of price change (since it's two months total they've been gone)
- 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.