People that wait until the last few seconds to put their maximum bid in. Good for the buyer, bad for the seller. I never knew Yahoo! Auctions extended the timing if someone pulled that stunt. Problem is, ePay has fostered this kind of worthless behavior. Sellers selling busted junk for too much money is another factor, which solidifies wanting to get a "good" deal on used wares bought there. Never fails. Your auction will sit there forever, with little to no activity, then during the last few hours, someone will bid. Closer to the end, people go nuts. Pretty aggravating all the way around.
I love it. If you don't want to get sniped, then bid the max you're willing to pay.