Unearthing this suggestion from the archives because it's still a relevant problem. I find trying to roll for max appraise to be painfully tedious and a chat-box spamming exercise depending on where you are. The process of opening the conversation, selecting the shop option, checking price, remove an appraise item if the price cap is bad and repeating isn't a fun or engaging experience at all.
My suggestion is just to automatically grant the highest possible sale price for a merchant based on your appraise vs. the shop's appraise. This would likely lower the maximum possible gold value in the event of your high roll vs. shop's low roll in the current implementation but it makes it straight forward and doesn't (at least to my knowledge) require editing every single shop NPC in every module.