If you're not in a hurry to buy them, I'd go to your nearest Sunglass Hut or wherever they sell oakleys near you and ask to try on some half jackets. That way, you'll know exactly what they look and feel like, and then would be able to make a comparison to your friend's pair. I find that a lot of people I know want to buy oakleys, but have never even tried on a pair. If you try one on firsthand, I can pretty much guarantee that you'll be able to spot a fake. No fakes I've ever tried (and believe me, I tried on a bunch during trips to DC and NYC

) have come close to the build quality of genuine oakleys.
As far as your friend's deal, a box, warranty card and carrying case is a good sign. I've known some people who just get tired of their oakleys and are willing to sell them way below what they paid. But if you're still not sure, ask to try them out for a day, take some pics and post them. If you do that, I (and other self proclaimed oakley aficionados

) can probably tell you.
If you're going to shell out that much money for a pair of shades, make sure you're getting the real deal. I've never regretted my juliets
