Users almost always raise their max bid, so it's best to snipe an auction to minimize the price. You can actually check the bid history of each item, with automatic bids filtered out, and you'll often see a long list of repeat bid increases from just a handful of users. Sometimes more than half the bids were placed by a single user.

If I really want an item, I snipe. I don't add the item to my watchlist, so other users won't anticipate my competition. But sometimes I don't want to put in that effort, or maybe I don't expect any other serious bidders, so I just place my max bid and move on.

But then someone outbids me. I reconsider, and yeah, I'll raise my max bid, but if they outbid me again? I'm gonna play a game. I'm gonna keep raising my max bid so it's the smallest possible increment above their current max bid. If the current bid is $100 I'll bid $103, $106, $109, and keep increasing my bid by the smallest increments ebay allows until I discover their max bid, and I'll sit right above that bid and wait for them to raise their max bid again. I know they'll raise it again, after all, the current winning bid is only a couple bucks above what they were previously willing to pay. I force them to overpay for the item out of spite.

It's a dangerous game.