Is he scamming? Minecraft premium account?

A used copy is worth nothing, as soon as the software hits the server it will show its' serial number. As a pre-used copy it will NOT give you a legal account.

Well if you look at the reviews on it, 2 out of the 3 say it's fake. And the third is probably the seller reviewing his own product on another account. I'd take the other two reviewers word on it and not waste your money on what is most likely a scam.