If it's American Airlines, expect the person who flies to get the third degree. My own husband bought me an award ticket with miles recently and I was questioned for a solid 15 minutes at checkin. About a ticket using points from my own husband. Who lives at the same address. And has done so for over 30 years. I just had to laugh because it was so idiotic that they questioned this.

If AA is that mystified that a husband would buy his own wife an air ticket with miles, they might find it hard to believe that mere friends would give such a generous gift without money changing hands. You'd better have your story straight. Personally I wouldn't try it. If something goes wrong, the friendship's down the toilet...

Since he's considering going into business selling the miles to multiple people, and some of those people probably have an unknown ability to handle being questioned, I'd say your chances of getting caught are nonzero.