In the case of a sale by auction

(1) Where goods are put up for sale in lots, each lot is prima facie deemed to be the subject of a separate contract of sale;

(2) the sale is complete when the auctioneer announces its completion by the fall of the hammer or in other customary manner; and, until such announcement is made, any bidder may retract his bid;

(3) a right to bid may be reserved expressely by or on behalf of the seller and, where such right is expressly so reserved, but not otherwise, the seller or any one person on his behalf may, subject to the provisions hereinafter contained, bid at the auction;

(4) where the sale is not notified to be subject to a right to bid on behalf of the seller, it shall not be lawful for the seller to bid himself or to employ any person to bid at such sale, or for the auctioneer knowingly to take any bid from the seller or any such person; and any sale contravening this rule may be treated as fraudulent by the buyer;

(5) the sale may be notified to be subject to a reserved or upset, price;

(6) if the seller makes use of pretended bidding to raise the price, the sale is voidable at the option of the buyer.