I had to do this once, too, with a similar reason - a
friend "borrowed" a video that I was selling without 
telling me, and the video got jammed in his vcr and he
basically tore it apart to get it out... however, I didn't
know you could cancel bids (there was one) so I simply
wrote the high bidder and explained the situation before
ending the auction (the high bidder was very nice about it,
too)... needless to say, that friend is no longer allowed
anywhere near my stuff...:P

If there are no bids on an auction, then there is no problem
with the seller ending it early (in my opinion).  If it has
been a few days the seller may also think that no one is
interested in the item.  I've also ended auctions early 
before when written with "I'll pay you this amount of money
(and there are no bidders) for the cel if we don't go 
through eBay."  If there are no bidders, then technically
you're not shutting anyone out because no one else has
laid claim to the item!  (If that person wanted it bad 
enough, they could've at least made a minimum bid to stay
in the game.)

I'm a little irrtated when I see bids cancelled and auctions
ended because the seller "didn't want to sell anymore" - 
this has happened to me before and I know it was just 
because the auction wasn't going as high as the seller would
like - but again, eBay doesn't consider the auction a
"binding contract" until the auction has been ended with
a high bidder.

Lady Z