AutoBid lets you set the highest price you're willing to pay for a lot. During an auction, the AutoBid system will automatically place bids for you in $1 increments until your maximum bid is reached.
If the bidding exceeds your maximum AutoBid, you'll receive an outbid notification via email. You can then increase your bid through your bid list in your customer account if you wish.
If you win the lot, you'll pay just $1 more than the next highest bidder, not necessarily your maximum bid amount.