> know about that. It's the same on eBay, seller 
> cancel the auction, because somebody offered
> them  a good amount of money or even a very
> good trade.

You are totaly wrong. An item on auction is not
sold until the action actualy closed. If the
seller consider that an item reached a buyout
price than there is no reason why he shouldn't
stop it earlier. Same for a trade : it just mean
that in the seller's eyes, the trade is worth more 
than your bid.

In fact, in many regular auctions, a seller may 
simply decided to cancel the auction if he 
consider that the price isn't high enough. (and I 
am not speaking of a reserve price).

When a shop confirms a sale to a buyer, the item 
is sold (pending of paiement). It normaly can't
be canceled without a very good reason. Canceling 
a sale because another customer offer more is not 
ethical and may even be illegal.

There is a big differance...

Cheers,
Yann Stettler