Bidding on an Auction site is no different than bidding at the courthouse steps. The Auction site is "brokering" the transaction for their client, most likely the bank or other owner of the property. The Auction site will get a cut of the action, just as a Realtor would, but because you are there bidding against others, you have no one to represent you or your interests.
At the auction, make sure you check out the property first with a title company, ask them to run a simple title search, normally about $25 to check out the property for liens and other title issues. After all, you don't want to purchase a house that has an IRS lien, a Hospital Lien and contractor liens.
My husband has "won" a few auctions for houses, and often the offers and bids do not get accepted because the bank or owner have set a "reserve" that must be met, when it is not met, they wait a few days and throw the property back on the site. So even if you miss the auction, it may still come back, just check every day and see. They are a great way to buy property and many investors use these as a way to increase their holdings.
Best of luck to you,