Value
The world of Stonetop has no central government, no common currency, and no standard exchange rates. So, what constitutes a fair trade?
To help answer that question, items and services are given a Value from 0 to 4. Value is more of a logarithmic scale than linear. A single Value 2 item is worth maybe a dozen or so Value 1 items. Three individual Value 1 items don't add up to Value 3; they're just three Value 1 items.
When you roll a 10+ to Trade & Barter, "a fair price" means you're trading within the same Value, but the exchange might not be 1:1. It might be 2:1 or even 3:1 if you're trading some common, local resource for a desirable or imported good (or vice versa).
If you roll a 7-9 to Trade & Barter, you might have to pay more or settle for less than usual. That often means a better or worse exchange rate (2:1 instead of 1:1, for example), but it could mean trading across Value tiers.
Regardless: if you don't like the exchange rate that you're getting, you can try to Persuade the other party to change their minds. Good luck!
Sawyl the tanner (your boss) confirms that beznpol hide is indeed valuable. "It's Value 2," says the GM, "but with a pair of hides, Sawyl could craft a suit of magnificent armor worth Value 3."
You've no desire to tangle with another beznpol, so you look to trade the hide away. This triggers Trade & Barter. On a 10+, the GM might say that there's a merchant in town who offers a pouch of silvers (also Value 2). On a 7-9, that same merchant might offer only a Value 1 item (like a fine steel spear), as beznpol hide isn't a hot commodity.
Alas, you roll a 6-, so the GM says "No one here is interested, and no merchants are due until autumn. But you could go out to Titan Bones and talk to the Hillfolk. Their heroes wear beznpol armor. They wouldn't give you a grown horse that's Value 3—but you could probably get a couple of Value 2 items."
Exchange rates are far from standard, but...