What is the difference between an auction and "pre-ordering"?

With pre-ordering, you are not certain of acquiring the domain even if you are the highest bidder. This can be because the domain was no longer for sale by the time the pre-ordering period ended. Or because the seller chose to auction off the domain at the end of the pre-ordering period. You will not be asked to pay for the domain in such case. Pre-ordering, also known as back-ordering, is mostly used for expired and deleted domains by NameJet and SnapNames. Bido also has a pre-ordering phase before each of its 1-hour regular auctions.