In truth, I don't think you could, and the seller has misrepresented the kit. That said, based on his email reply I think he was genuinely unaware (ignorant?) of the difference between a HobbyFan kit and an original Club-M.
If it really was a Club-M, you would expect the starting price to be around US$500. His starting price was about right for a recast.
Not sure if that helps, but if you bought it expecting an original Club-M you should contact the seller and you'd have grounds to rescind your bid.
HTH