Quite right, its remarkably easy to retract a bid.
Just had another one today, I was selling some parts today and someone bombed the auction in the last minute, fair enough not complaining, he then contacts me to say "I am not paying, I entered the wrong amount and didnt put a decimal point in the right place". Fair enough I thought, send a cancellation through and offer to the under bidder. The under bidder then gets back to me saying that I should offer him the parts at half price and INCLUDE the p&p as well. Seems very fishy to me, and both now added to my black list. Does this sort of thing happen a lot?