I'm guessing the guy removed the ribbon that would prevent a legit Zeraora from being WT'd, but if you can't trade it now then I'm not really sure about what to think. If you could upload the Zeraora as a .pk7 file, or at least show us screenshots of it, we might be able to tell.
Regardless of that, though, I do recommend you to release it, along with anything else you might've gotten from him.