We are reasonable people.  If it's an apparent typo we'll contact the bidder to confirm and then correct the bid.  If it happens in last moments before winning bidder is declared, we keep the bidding open (or roll it into an auction closing the next day) to allow a natural conclusion and be sure all the bidders participating on that asset know what's going on and why.  Very much like you'd see at a traditional live auction . . . 

Although there is a bid confirmation screen that is supposed to slow folks down to re-read what they typed, one still gets through occasionally.

Jerrod