Unfortunately, I've had this happen recently on one of my vintage bike eBay sales. The 2nd highest bidder received an official-looking eBay "2nd Chance Offer' e-mail from some crum in Europe. The bidder had the presence of mind to contact me through eBay about the bike, which, of course, had sold.
It seems you're OK as long as you send e-mails through eBay. FYI: They don't keep track of anything said in these e-mails. I'd say eBay barely has the staff to collect all the money that's falling into their hands, let alone police users or go after thieves.
Next: Any Bridgestone experts here? I'm still trying to determine the story behind my '89 long top tube RB-1. Why has it got a 59cm c/c top tube on a 58.5cm c/c frame? It should be a 57cm tt according to the literature.
Jim Hultman
Santa Barbara; still 70 degrees & sunny.