[Pseudonym]

The way I play it is that they just don't know how much its worth. This means they can't make (as educated) a decision as to whether they should take or leave a 10 lb collection of books that they find in a dungeon, or if they should take the 10 lb copper figure instead.

That seems a bit lenient, but vexing; though by RAW, it feels like they are guaranteed a certain return for selling anything as long as they don't risk any reaction rolls or merchant quick contests. I might add the success/failure of a price evaluation as a complementary modifier for those rolls if they want to be chancy, meaning that in the end, for someone with absolutely no reaction modifiers, it improves their odds in the positive direction something like ~10 % (less if they have a high or low reaction to begin with) I guess, which is not nothing, and probably something like ~15% for the quick contest, where even a small difference in effective skill makes a big difference.