Not only is it annoying to the bidders but it is 
also to the sellers.  This happened to me a few 
times when I was selling off a few of my cels... 
and you know, many of us collectors don't have a 
whole lot of cash to spare; at least I don't.  
Selling my cels gave me a little bit of money 
that I really needed and when a high bidder went 
back on their contract (placing a bid on any 
online auction is a CONTRACT--you legially agree 
to pay for an item), that just lowered the price 
of a cel that I was expecting to get a little 
more for.  Sure it usually doesn't amount to 
much of a difference, but when you have very 
little money to begin with, every difference 
counts.  So besides the money issue, it's just 
plain annoying when bidders go back on their 
contract, and sometimes you may not have another 
bidder to fall back to.  *sigh*  If you don't 
know whether or not you really want the item or 
if you can pay for it, don't bid.  Plain and 
simple.  =P