Since you have not communicated yet (two way) with the seller and have no idea what his circumstances are, I would move on. He is only guilty of not returning your message; he has not stolen your money or shipped you a box of rocks instead of an AP 900.
Since you asked, my opinion is that you have no standing yet for giving him a rating at all.
Since you asked, my opinion is that you have no standing yet for giving him a rating at all.