> Sure, the party isn't expecting the local innkeep to make change for a platinum piece... but nobody else can either. It's like trying to pay someone with a barrel of crude oil; sure it's worth a lot, but what is Bob the Fishmonger going to do with it?
Same applies to objets d'art, handfuls of gems, and rare/ancient/foreign coins. Finding someone who can evaluate and buy their stuff could be a fun RP adventure, and there are all kinds of stories you can tell around an auction house.
http://rpg.stackexchange.com/a/22602/4398