As it was a legally binding contract , would the buyer be able to take the seller to small claims court for the item at the price they won?
I guess theoretically if they had refrained from bidding on another sale of the same item because they were winning the OP's, and were now only able to purchase the item at a higher price, they'd potentially have a claim for loss of bargain. Of course proving that would be problematic, not to mention the amounts involved would probably make it not worthwhile