This is from AS' faqs:
65. What happens if I am already the high bidder, and I snipe against myself?
This is one of the most common questions that we receive. Here is the answer straight from eBay:
"In most cases you, as a bidder, cannot bid against yourself. However, there are a few exceptions where this can occur, and I have listed these incidents for you below.
Let's say you are tied with another bidder and you hold the official high bid because you placed that bid amount first. If you place another bid, you will lost your favored "early bird" status. As a result of putting in another bid (causing you to become a later bidder), the system will increase your bid to one bid increment more than the previous bid just so that you can keep the position of high bidder.
Another instance where it would appear that you are bidding against yourself would be if your current high bid is between bid increments. If you were to place another bid, your bid will increase to the next round bid increment.
The high bid will always try to be a full bid increment over the next highest bid. If you are currently less than one bid increment over the next highest bid, then raising your maximum bid will increase the current high bid to a full bid increment above the next highest bid.
Also, in a reserve auction, if you are the current high bidder and the reserve still has not been met, your bid may be raised if you place another bid that meets the reserve amount. On reserve auctions, if your maximum proxy bid meets or exceeds the reserve amount set by the seller, the system will place a bid so that the reserve is met. This allows for an auction to be ended successfully."
