Check: The character makes an opposed roll against the merchant's appraise skill. If the merchant wins, the character pays more for the goods in the store. If the character wins, he pays less. The first time the player interacts with a merchant dictates the prices in that store until his appraise skill improves.
Before the expansion packs were released, store prices were fixed (no die rolls). A patch added the die rolls to the original campaign, even if neither expansion was installed. (A PC cannot buy ranks in appraise if neither expansion is installed, but intelligence will still influence the rolls.)
Unlike other skill rolls, this opposed roll uses a d10 (10-sided die).
The prices are adjusted by a percentage equal to the difference in the die rolls, subject to a 30% cap.
As noted in the description of the check, an appraise roll is not made when re-visiting a store unless the player's appraise skill has improved, not changed. A lowered score does not trigger a new roll. Thus, a character does not need to equip appraise-enhancing items every time a store is visited; wearing them as the store is opened once is enough to gain their benefits for future visits to that store. Similarly, casting fox's cunning — or drinking such a potion — to improve appraise can be done for just the first visit to a merchant.
Note that this skill is script based and it might not work in every community module, especially the really old ones.
A module builder has the option to change how the skill works by using module-specific scripts.
Builders should be aware of the appraise check and be wary of setting a merchant's mark up and mark down rates so close (within 60) that a character with a high appraise skill can buy items for less than what the store will pay to buy them back.