If the seller cancels the auction (by cancelling
all bids and closing it early) for whatever
reason (ie. item is no longer for sale, 
description isn't accurate, etc.) then the seller
is no longer obligated to sell the item to 
anyone who bid (whether or not you are the 
high bidder currently).  

Until the auction closes, there is no "finalized
transaction", and the item is still the seller's
property to do with whatever he/she wants.  Once
the auction closes, he/she is legally bound to
sell the item to the winning bidder.

Basically, if the seller chooses to accept an
offer and cancels all bids / closes the auction,
he/she can sell it to whomever he/she wants.
However, eBay probably would NOT be happy to find
that a seller misused their site by gaining 
attention to the item and then just sold it
privately (therefore avoiding eBay fees, which
is what would make them mad).  But how would you
prove it?  He/she could just say that he/she
changed mind about keeping the item.

Hope this helps.  =(