"bust them"? For what?

Unless you're in an area where such "scalping" is illegal, there doesn't seem to be any violation of the law on the part of the travel agency (broker).

There may be a contractual violation of the T&C of the Frequent Flyer program by the person selling the miles, and the airline could certainly try to take action against that person if they track him down (which they might be able to do by buying a ticket from the broker, but that's just catching one individual, not "busting" the broker), and they may be able to refuse to honor the ticket tendered by a buyer if they can establish it was obtained in violation of the terms of carriage, but I'm not sure what they could do against the broker. Doesn't seem to be any privity of contract with him, either as Frequent Flyer account holder, or person who is tendering a ticket in exchange for transportation.

That's not to say I suggest anyone do it, I just can't figure what the airline could do legally to the broker if they catch him/her.