Something tells me you don't deal much with CL. That's why people meet at starbucks rather than at home, to avoid intrusive weirdos who insist on taking pictures and copying IDs.
I was thinking more along the lines of receipt, proof of registration, etc. Photographing their license plate does nothing for you in terms of avoiding buying stolen property, and the people suggesting that or photos are not thinking. The best thing you can do is attempt to verify a valid purchase. If you can't verify that, it's perfectly fine to walk on the deal. You could even meet them at the genius bar if you're near an Apple Store. They can obviously verify registration and make the necessary changes.