I found it. Seller has 50,000 feedback and has sold over 10,000 of these.
Buyer is very very protected on eBay (to the detriment of many a seller) so I cannot see how this would not be legit, provided you buy from the listing and pay with PayPal.
If you get a box of rocks you get your money back.
If you don't get exactly what is described you get your money back.
If you are a jerk and just want the free use of a MacBook Air for 90 days you can claim not as described, return it and get your money back.
Sorry, but I was burned by too many buyers and am cynical but you should be fine.