On rare occassions someone who has placed the winning bid will contact the seller before the auction ends and ask to have their bid cancelled.  The seller may not see the message in time to cancel the bid, but they may still cancel the sale, "at buyers request" after it is all over.  They are then free to relist the item.

If you suspect "funny business" you can call eBay customer service and ask them to look in to the matter.