It has been reported to us that some of the Gmail sales on eBay may be less than legitimate. According to one poster on the Blogger Forum, he purchased what he thought was a Gmail invitation and all he got was a link to us here on the Gmail Exchange forum.
Not a very good purchase since probably only about 10% of the requests for Gmail can be filled. Some people will do anything for a buck.
Incidentally, there are about 4800 listings in eBay under "Gmail" at the current time.