Don't forget, you can do a user info request and get their
phone number.  I have done this a few times when their
email was down, or they were "unresponsive" to a high-
dollar winning bid notification.  Nothing shakes 'em up
like an actual voice call, and surprisingly even the goofs
usually enter their real phone numbers.

The URL to that page is here:
http://cgi3.ebay.com/aw-cgi/eBayISAPI.dll?MemberSearchShow
 
Just to stay "OT"  _   I will add that cel buyers on ebay are
MUCH more mature and responsible than many other categories
(like action figures, etc.)  Usually I get 100% returns
when I sell multiple lots in a given week.