I have developed a philosophy when bidding on items on eBay: first of all, I try to decide how much I really want the item. If it's a one of a kind or I've been looking for a while, obviously that will be more.
Then, I just set a limit on how much I am willing to pay. For a given item that might be had at retail for $150 and is now at $120 on eBay, I calculate possible shipping costs, then make sure they and my bid don't go past $150. Then I don't worry if I win or lose, because it's karma. I won't kick myself for not having bid more, because I went through that argument with myself beforehand.
Auction Sniper just makes all these things so EASY!!!!! The only auction I lost with AS, I knew I wasn't willing to pay that much for.
And that's one out of maybe 25 auctions I've won so far . . .