The amount above the hammer price that is paid as part of the total purchase price. See Sotheby's Buyer's Premium rates here.

An advertised percentage of the high bid added to the high bid to determine the total contract price to be paid by the buyer.

An additional amount added to the hammer price of something. It is paid to the auction house for its services. On the auction, the price list will note whether the prices of art include the buyer’s pr [..]