So I found an ad on kijiji, for a 2012 MBP (assuming this is a retina?) He says he doesn't know anything about macs, and that's why he's selling it. But get this...it's only $850. Too good to be true? We'll find out He said its a 15" i5 with 4GB of ram, but doesn't know anything else about it because he's technologically inclined. Other than where the power button is located,how can I tell this is a 2012 model? We will be meeting at an Apple store to make sure it's legit and not stolen, I suppose I could ask these questions there, but I'd rather save time. Thanks!