Ugly situation! If you want to avoid it, I would 
say that doing the pre-approval thing is a good 
idea, but just make sure to put your auction on 
for a full 7 days to give people plenty of time 
to send in their requests. And you may have to 
babysit the computer the last day of the auction 
to deal with last minute requests, so that you 
get as many bidders as you can. The other option 
is simply to contact the second-highest bidder 
and see if they want to buy.