There's always a certain risk to buy such things over a platform like Ebay. But seems that the seller already has been active for longer, having positive reviews & even offer warranty (even though idk how that works on ebay). The price is rather cheap - but you probably won't be able to sell such a N9 for over $300. So overall that offer looks all right to me.

The Chinese & Finish production don't vary significantly - to the end-user it's the same product of same quality (we're talking of course of original phones ;-) ). What could be a problem is the installed firmware: In case it's the Chinese one you won't have any Facebook, Twitter & co. A firmware flash to another country code would be necessary.

Good luck with your decision - but if you feel it's to risky, rather pay some more and get it from somewhere else.