I have purchased 2 scopes on Ebay: Bushnell Elite 3200 and Burris Fullfield II. If memory serves the Elite ran @$150 and the Burris almost the same. They were lightly used, nearly brand new, and advertized as such. Excellent scopes, excellent people selling them, all very satisfied on both ends.
As with any sight-unseen transaction, there is a risk involved. If you don't want to take that risk, stay away from Ebay. I would characterize that risk as being very small, considering the feedback ratings of the vast majority of sellers on Ebay. In return for the risk, there are sometimes reasonable bargains to be had for the discriminating buyer.
In dozens of transactions on Ebay and other internet auction sites, I have never dealt with anyone who was dishonest or wouldn't correct a mistake they've made. That said, I'm sure there are going to be a few bad apples in the bunch.
I personally stay away from sellers who don't try to give you a detailed assessment/description of their product, including pictures, up front. I also won't buy from those who are overly demanding or unreasonable about shipping, payment, etc., and of course any who have a questionable ratio of negative feedback.