Black sunglasses cheese

How do I know my Tiffany's is real? - photos of tiffany towers

I bought a diamond bracelet on eBay for $ 40. It came with the "Green Box" little by Tiffany's jewelry case and bracelet.
My friends say that for that price .... not really, but what makes me believe it really is the guy who recommended the sale only as a "silver bracelet, and how (the sellers and) not in a store and Tiffany was not even mentioned that one. He just said: "sell silver bracelet. What makes me think they knew what it was worth. I knew it was Tiffany's in the photo.
How can I check to see if it is real or not?