I am totally not recommending you to buy from this seller.I doubt this is a low quality domain,also they do not use ssl security .
They are even not able to manage ssl security on their domain,how can they afford to sell such an expensive machines?
You can simply go and buy from bitmain's official website without risk.Exactly, he could buy directly from bitmain! he probably is the owner of that site trying to scam/trying to get customers to sell the products at higher rate.