Auction sale rules: reserved bidding permitted only if expressly announced; fictitious bidding renders the sale voidable. Auction sales treat each lot as a separate contract and the sale is completed when the auctioneer announces completion, typically by the fall of the hammer; bids may be retracted until that announcement. The seller may expressly reserve a right to bid, and only then may the seller or an agent bid; without such notice seller bidding or employing bidders is unlawful and may be treated as fraudulent. Pretended bidding to raise price makes the sale voidable at the buyer's option.