Strategy 1: The Incremental (aka. Lowball) Bid
... If the bid is placed early, and the lowballer has the high bid for days, they could gain some emotional attachment to the object. The danger here is that they could very well be outbid in the late stages of the auction.
... By bidding early, other people who collect the same thing that you do could perform a search of your ID to see what you are bidding on. Then, they will follow you around from auction to auction and bid on the same item that you are bidding on. You do all the work, and if they have deeper pockets than you, they will get all of the benefits of it.
Strategy 2: The Proxy Bid
... There is one scam that allows someone to sniff out a proxy bidder's maximum bid. Someone could bid ridiculously high, taking the lead by one increment. Obviously, they could deduct by that lead what the proxy max is. Then, they retract with the "wrong amount" excuse.
Strategy 3: The Time-Awareness Bid (aka, the Snipe)
... If you snipe, you may receive e-mails from some very unsportsmanlike individuals belittling you for outbidding them. True, you still have won, but it can be annoying.
By the way, sniping is when you place your bid mere seconds before the auction ends, thus preventing anyone else from counterbidding in any way. You can autosnipe with a variety of sniping bots (google:ebay sniper).