Not happening, its a security feature so only the original owner can wipe or unlock the phone. Then you can put in your own icloud password and set it up as yours, but only after the original owner has ok'd it. Its a great feature so that even if the iphone is stolen, it blocks anyone else from using it.
I would give the ebay seller a bad review for sure because he is probably selling stolen iphones. If they said its icloud locked then its your issue for not reading it clearly.