any time there is a request for a photocopy of a credit card, and very specifically the BACK, its bad news bears. teh back number on your CC should never be revealed to anyone, and if anyone asks you to read it, you deny. the only exception is when you call visa or activate a card. even then they might not ask for it. there are other times but this is not one of them.
if they're legit, you give them your CC number and they charge it. its pretty standard stuff.
also. 100% of companies charge your CC first, and when it clears, they ship. pretty stupid if they don't.
last word: if it seems to good to be true it usually is................