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=An advertisement that some item or other will be sold by auction is normally an Invitation to treat, not an offer. The bidder makes an offer which the auctioneer can accept or decline. However, if an auction is without reserve, then the auctioneer must sell to the highest bidder, that is, he makes a unilateral offer to do so to the highest bidder. This offer is in addition to the offer made by the bidder to the auctioneer. See Warlow v Harrison (1858) and Barry v Davies (2000).