I looked at his ebay evals and most of them are very small amount purchases/sales, which is common in scammers who like to up their feedback quickly so they can appear to be "legit." also of notice is the fact that none of his previous sales were imacs.
I would recomend requesting either that you set this deal up through an escrow(you pay the money to it, he delivers the product, you say product is ok, he gets the money), or do a COD. Offer to pay the fees, as this is a very good deal if true, so the little bit extra won't hurt. If he declines, chances are he's a fraud.