It's a psychological thing.
Say for example (taking the two people's names I can see directly above this window) that Muban is selling something that both DiG and I really want.
I'm prepared to pay a tenner for it. DiG doesn't really know how much he wants to pay and hasn't thought about an upper limit. He puts a bid on for a fiver a couple of days before the auction.
I know that I'm not prepared to pay more than £10. I set a maximum bid of £10 shortly after DiG has placed his bet. Because of the way eBay works, it increases the bid to £5.50. DiG sees this, thinks about it and bids £6. My bid is automatically increased to £6.50 and so on and so on. When DiG bids at £10.50 it overrides my bid and because I've set my maximum and walked away he wins the auction.
Alternatively, DiG puts his bid on for a fiver. I set my sniping software to put my maximum bid on of £10.
Five seconds before the end of the auction, my bid of £10 is placed. Because of how eBay works, DiGs bid of £5 is beaten by my bid of £10, but the bid of £5.50 is all that is placed.
I win the auction for £5.50 because DiG hasn't had a chance to see my bid and respond to it.
I'm happy because I've won the auction at less than I was prepared to pay. Muban is happy because her item has suddenly had an increased bid at the last moment. DiG is annoyed because I outbid him in the last few seconds.
I think that explains it.
Right now the serious stuff - What were you auctioning that I just won for £5.50, Mubs?
K.