I have bought a lot of scuba gear on ebay, I have not yet (knock on wood), been burned. I gotten one item not quite a nice as I thought, but my fault as I didn't look close enough to the pictures. for the most part what I have recieved has been better than the pictures can show. But I always check out the sellers rating and feed back.
I have bought; BC, several regulators(primarily vintage), guages, tanks and wetsuits (several as you probably know manufacturers are all different as to sizes). the beauty of the system, what doesn't suit you can be reposted. Good pictures and adequate description can quite often even turn a profit.