Most of the new bikes on eBay - more than half - are Bikes Direct. 60% are not stolen. There are a lot of fraudelent sales that get on eBay but are taken down after a day or two and most likely never get a buyer. They usually require payment by certified check or some such means, and many are from UK.
As far as sales of new bikes from sources within USA and fraud on eBay - would have to be way lower than even 1%.