Definitely make sure that the person who made you 
the offer is the high bidder. Not only does this 
assuage some of the people also bidding, but if 
the auction closes with the person you're dealing 
with as the high bidder, then you will be 
protected as a seller under Ebay's rules. (If 
they're the high bidder, it's no longer 
completely a private deal - even if you made a 
deal with them for more than what their high bid 
turns out to be.)

Many Sharp Smiles,
--Drac