Lowest? Don't you mean highest?
Auction rooms only accept telephone bids from established customers, or from people they know they should be able to trust. (They won't usually accept such bids from total strangers). If the bidder fails to pay up they have breached their contract with the auction room, meaning that the auctioneers can sue them to get their money.
Auction companies do everything they can to make sure that they get their money. I was once pursued, by a firm of auctioneers, for money they said I owed them through a successful bid which I'd failed to honour. After a lot of hassle and threats of legal action they eventually accepted my (truthful) assertion that I'd not even attended that particular auction and that someone else must have quoted my account number (or that the auctioneer had misheard it or incorrectly recorded it).
Chris