Though we should note this only works in the absence of collusion. If a bidder colludes with the seller, then they can increase the amount the highest bidder pays by bidding a very high second-highest bid.
If the bidders collude, they can get a very low price. This is (obviously) true of most auction systems, but for sufficiently public English auctions, bidders that are otherwise uninterested in an item might bid on an item that is going for obviously far below market.
