called unreserved auctions. Reserved auctions are the same except a minimum price or "reserve" is set to ensure the stamp does not sell below this level. If during the auction there are no bidders for the lot at the reserve price then the lot will be left unsold in the auction.

Buying at auction takes knowing the market and what stamps are worth at both a wholesale market level and what they can be then sold for in a retail market. Stamp values are heavily skewed to quality. The same stamp can sell for drastically different prices