Even sellers who do have 100% feedback and have sold hundreds of items can be dodgy.
I worked with a guy a while back (who did, incidentally, end up in jail) who was flogging HEAPS of computer gear from the place we worked. It was all legit (in the sense that it was actual goods that the people received), and his customers were happy. Months later, some of the items were recovered as stolen property...despite people buying them, and leaving positive feedback.
He stole around $150k worth of gear and flogged it for about $70k on the bay.
As always, BUYER BEWARE.