I know there's a older thread on this somewhere, but I don't have the search feature...
There are quite a few real life examples of this. My recent one is with used video games. I recently traded in a bunch of old games for store credit and one of the games netted me $2. It was an older Xbox 360 game that had the instruction book and case and played just fine. Not many used Xbox 360 games sell for under $10 at this location (some, but not many).
Now, I have no doubt that if I looked I could find someone to buy the game for more than $2. I simply didn't want to bother with tracking down said individual, and even when I did find some one interested who is to say they would trust me (a complete stranger) enough to pay an amount that made the effort of the search worthwhile?
Used Text Books are another prime example and don't even start to look into the pawn market or jewelry for trade ratios better than 20%.
There is nothing stopping the players from holding onto something for a better price. There is nothing stopping the DM from making said search into an adventure itself.