We've seen a couple threads here over the years where people have got caught at the check in counter ("look at the great deal I got"), so there is some risk when you sell miles (although I recognize you haven't had any problems). If someone using your miles made that statement to the check in agent, how are you going to respond when the airline calls? Do you get some type of background packet on the person that will ultimately be using the miles, so you can cover for each other?

Why not just a cash rebate credit card to work around all this?