Just to clarify some auction terms:

Hammer price is the final bid on which the auctioneer brings down the hammer. It does NOT include the buyer premium.

The Buyer Premium is a commission that the house charges the buyer. VAT is collected on this regardless of where the item is shipped and this VAT is NOT refundable.

The house also charges the seller a premium but that is another issue. The house will also charge the seller for illustrations, insurance, storage, cataloguing and anything else it can think of.