Does this seller seem legit?

I say Chinese fakes. You can tell because he has already sold over 500 of them and Apple does not allow ANY of their authorized retailers to sell on Ebay. ONLY official Apple retailers can buy in bulk, and he's not an official retailer.
The fact that he even states it does not come with an Apple Care warranty means they are not real iPhones because All iPhones come with an Apple Care warranty
He also says they won't work with Verizon or Sprint. Again that's because Verizon and Sprint will not give contracts to fake iPhones. If they were real iPhones you would be able to get a Verizon or Sprint account with no problem

Have a look at their negative feedback. All complaints are about phones NOT being unlocked, NOT all original parts, etc.