I've had a look at their listings, and also chased up the domain name registration of mobybicycles.com.
Looks extremely bogus - the website appears to have been thrown together overnight, and the domain name registration is relatively new. If you read the 'customer testimonials', you'll find that they are all written in the same manner, grammar, etc, which again looks like one person sat down and typed up the testimonials.
And besides, on eBay they claim that their 3rd party escrow payment service is much more secure than PayPal. I know PayPal isn't perfect, but it offers punters like us a decent level of protection in case any transaction goes sour.
Moby Bicycles? DODGY! DODGY! DODGY!