If they have a valid CD and key, I use their CD and Key.
If they dont have a CD but only have a Key, I use my CD and their key. My CD is used over and over.
If they dont have a key but they have a CD, I make them buy a key (extra cost on top of the format work)
If they have neither, I make them buy the CD/Key (once again, extra cost on top of format work). I buy these CD/Keys at my supplier so they are about $45 cheaper than the retail price, I then sell them at retail price.