This is exactly what faced the owners of the Dollsville Dolls shop in Palm Springs, California, this week. Evidently, an eBay user intending to fraudulently sell electronics got hold of Dollsville's account information, and put up these auctions for expensive electronics without Dollsville's knowledge (they tried to funnel questions and contacts through another e-mail address). Dollsville then spent the next 12 hours desperately trying to unravel the whole mess with eBay.
Unraveling the mess proved to be stressful, since eBay funnels this sort of request through their Live Help. Live Help is a help service where you type to technicians via the Internet. This made the process of having the auctions taken off of Dollsville's account much more difficult (and stressful) than it would have been than through straight phone technician help (although Dollsville did speak to at least one eBay employee via phone).
The good news is that the fraud was discovered early, was taken off of the eBay site and off of Dollsville's eBay ID. The bad news is that this happened at all, that it disrupted Dollsville's legitimate business and doll customers (there was a temporary freeze on their account while this was unraveled) and that there are no "real" people easily available at eBay via a phone call when something this dire happens. I do know that eBay is working on providing more live help for eBay customers, and it should be a top priority for eBay--this sort of fraud undermines both buyers and sellers on eBays and creates an atmosphere that leads to less trust and lower prices for legitimate eBay sellers.
If you are a seller of dolls on eBay, remember to check your eBay account from time to time even if you are NOT actively selling dolls--think of what could have happened in this situation if Dollsville had been away on vacation for two weeks when the account hijacking occurred. Also, be alert for any e-mails that ask questions about odd items. Don't ever, ever send any eBay account information or passwords via e-mail (Dollsville didn't do this, but this is a way that YOUR eBay or Paypal account could be hijacked). Make sure that your computers connected to the Internet have firewalls, as well as appropriate spyware and virus protection. Be vigilant when you are on wireless networks that can be accessed by others. Finally, have difficult to guess passwords which include both numbers and letters and are a minimum of 6 characters. Although these security precautions did not stop the account hijacker from hijacking the Dollsville eBay account (they still do not know how the account was accessed), these hints MAY help prevent someone from hijacking yours.

