Easiest way to tell a real (vintage) pair of ray bans from fakes is to check the lenses. If they are genuine B&L glass (tap them with your finger nail) and have the initials "B&L" incised on the left side of each lens, they are original.
After about 1995 the Ray Ban brand was purchased by Luxottica Group, and all production moved from the USA to italy. The frames made in italy no longer carry the B&L logo on the lens, which are now made of polycarbonate. However the contemporary fakes are usually pretty easy to distinguish by the poorly printed and place "Ray-Ban" logo on the lens. Plus, they usually carry plastic lenses instead of polycarbonate, which is also distinguishable by the sound they make when you tap them with your nail. Good Luck!
Also, here is an decent eBay guide http://reviews.ebay.com/Identifying-Fak ... 0001827218