I agree with those who counsel against this. US is good at filling seats right up to door closing (and will delay door closing on occasion to fill seats), so it has a good chance of not working.

I'll leave aside the ethical considerations and move onto the question of fraud and detection. What role does intent play here? Just as there are "hidden cities" and there are "hidden cities" ... Surely I am not the only one here with the relatively benign circumstance:

I am a committed FT. I am planning on going somewhere. A less dedicated family member expresses an interest in going, but is not totally sure. Fine; I buy myself my typical nonrefundable ticket. There are some markets where the refundable tickets are not so much more expensive -- if I happen to see that we are in that situation, this is a reasonable solution: I buy a refundable ticket for the other parties and, yes, we book seats next to each other. (I'd keel over the day we were not charging all of these tickets to my credit card, too.) I'm not an economist, so maybe I can't distinguish fraud from hedging ... Does a hedge become a fraud when my subjective probability of the future behavior of my potential travel companion dips below 0.25 ? When I fail to cancel until the day of the trip ?