I have a few. But this is one that bugs me the most.
I make an offer for a page of art to someone, and they decline the offer saying it's not enough, and then don't counter with an amount they would be willing to sell for. Not even after I ask them to. Mind you, this is for a piece they are ADVERTISING IS FOR SALE AND ARE INVITING OFFERS FOR. Not an "NFS" listing on CAF. If you are advertising a piece is for sale, and someone makes you an offer on it - and you decline - that usually means you are supposed to respond with the amount you want to sell it for. And, negotiations ensue. If the buyer thinks its too high, they may decline to make another offer. Or, they may make another increased offer hoping to compromise and complete a deal. But, refusing to say how much you want to sell a piece for - hoping the buyer magically reads your mind, or continues to bid against himself - is kind of annoying.