I'm about 90% sure I'm right about this. But I think he keeps bidding because someone else is bidding, but doesn't beat his maximum. For example, I bid $100 on your item, but it starts at $25, so my bid shows up as $25. Someone else bids $30, so my $100 bid still beats his, so ebay automatically puts in a bid for me for $31. I'm pretty sure that ebay only shows my $31 bid because his bid doesn't really count since he never beat my original bid for $100. Only if he bids over $100 will his bid show up.