We buy houses on Auction.com every couple of months and there is always a reserve price that needs to be met. The "winning" bid will go to the bank and if it does not meet the reserve they will counter with a much higher one. You then have the choice to accept the counter or let it go and get your money back.
If you track a certain property you can usually see it go through a few cycles and get a good idea what the bank is looking for. Some of the other auction sites will say whether the reserve has been met and sometimes you have to bid against yourself to meet the reserve since the banks counter can sometimes be higher than the minimum reserve.
Just like ebay, most bids stay low until the last half a day or so and then they start taking off. It is not uncommon to see properties go up tens or hundreds of thousands of dollars in the last few hours depending on how many people are bidding and which ones have "automatic" bid raises in place.