An irrevocable bid is when the auction house finds someone who promises a certain amount for a distinguished work of art. If no one bids any higher, then the bidder gets the work, paying the normal buyer’s premium. If it goes higher, then the auction house shares the upside with the bidder, in an arrangement that may be 50/50 or on a sliding scale. However, while some auctions reward the third-party guarantor just for participating, others only pay out when the work goes to another bidder.