Said brokers advertise in the classifieds of USA Today. I sold a 20K award to a Miami broker for $300. A few months later I tried to sell one to an Idaho-based broker, booked it as an E-Ticket 8 days adv., didn't get a check, so I called the airline the eve. before the AM flight to cancel. I was out the $35 fee but saved my miles.
I tried to complain to IDaho Atty. Gen., but I had no name, only a phone #.
Above points are right--if they cheat you, you have little recourse. It's like going to the cops to report that your dope has been stolen.
BTW, if you sell/give to a friend, include a birthday/Christmas note from yourself to the flyer. Just in case the airline ?s something.