Some buyers don't understand theautomatic bidding system, and keep on nibbling away with multiple small bids until they have outbid the current high bidder.
Some do it more strategically, to intimidate other bidder into thinking that there's no point in bidding, as they seem sodetermined to win it. This is called bid stacking, but there's no evidence that it works.
Both areperfectly legal, there's nothing to "police".