I'm with eigenvector on this.

There are legitimate FTers who have had their accounts frozen for GIVING flights to friends and family, because it was SUSPECTED they were selling them.

Sure, it's not your account that will be frozen/closed, but if that happens, the tickets are gone.

I think in my history of booking flights for other people, there has only been one case where the person did not meet one of these three criteria:
1. Was not on the same flight as me
2. Did not share my last name
3. Did not have the same address as me

But I've certainly spent enough miles on other people that if those criteria didn't match, flags would have been raised.

And I've certainly had a balance high enough to sell $20k in flights.

Just don't risk it.