I'm in Times Square shooting the Imagine Cup event, and several people said that to fix my shot, I would need a faster lens. Just for the hell of it, I went across the street to a photo shop to see if they had the lens, and what they would be willing to sell it for. The price they quoted though, is kind of unbelievable. Particularly given that on Manhattan Island I would expect pretty much everything to be more expensive.
I'm concerned that I would be walking right into a ripoff of a refurb'd, used, or "grey market" lens. But I don't know enough about what the legitimate lens looks like to tell. What things should I look for to distinguish a legitimate lens from a fake one?