You need to treat the zero feedback bidders
like everyone else.  Even if the bidders have
several feedbacks, it doesn't mean he/she is 
reliable.  I have some cases that the bidders have
about 5-20 positive feedbacks, but they still
don't want to reply or send the payment.  What
can you do...other than selling it to the second
highest bidder, or you can get the money back 
(except insertion fees) from EBay.  Of course,
for the people who don't reply or send money, I 
leave them negative feedbacks.  But anyway, if
you didn't hear back from the bidder, email 
him/her again for a couple more times.  I have
a few cases that the bidders will just send you
the payment without replying you in emails.  Just
wait a couple weeks to see if you can get any
email reply or payment.