I've never held a private auction, so I'm not too 
clear with exactly how the identities are witheld. 
But I'm gathering that even the seller doesn't have 
access to the identities, feedback, and/or email 
addresses of the the bidders. If you do have 
access, and the high bidder does flake, you can 
always offer it to the next in line. If second in 
line is legit, remember he was willing to pay very 
close to that high bid. I wouldn't cancel the 
auction. See it through and maybe the bidder will 
surprise you. You do have a reputation for offering 
some nice and very sought after DBZ cels on ebay, 
that alone might be hiking up the bids. 

"A cel from Misa?! I'll pay anything!" ^_^

Worst case scenario, you can relist and still get a 
good price for it. Best case, you're making a 
niiiice profit, let yourself enjoy that. ~_^

MeganD.