In some cases, it might appear that a single bidder is bidding against himself. For example, you might see Bidder A bidding $10, $12, $14, $16, and so on, with no one else bidding. Nothing fraudulent is going on!
Most likely, Bidder A is causing this effect by bidding against Bidder B’s maximum bid. Bidder A is trying to find the point where his/her bid will outbid Bidder B’s maximum bid by manually entering small bids one by one. When the maximum bid price of Bidder B is exceeded, Bidder A will have a winning bid.