I have also found several of these on eBay; Here are some things to look for:
1. The price is too good to be true
2. The information is vague about where the bike is
3. The seller is not in the same location as the bike, and is usually registered in a another country
4. The seller has a history, but it is usually a bunch of small, unrelated stuff (developing a history on cheap items in preparation for the scam, or stealing someones history?; not sure on this one)
5. The seller will not accept escrow payments, etc. and wants a lot up front money.
6. The seller insists on wire transfer (something eBay cautions against the ebay guidelines on this topic are very good, by the way)
7. The seller frequently offers free shipping anywhere (on a bike? Get real).
In general, real bikes on eBay can be had for good deals at times, but not great deals. A lot of people are looking at them and will bid them up. I have bought two bikes on eBay, and it worked out well, but again, the deals were merely good, not great.