I learned my lesson back in the 80s with United. Sold miles to a PDX ticket broker and was later notified by the airline that the end users had their tickets confiscated in Hawaii. They had to purchase returns at full fare. I got off with a warning---Whew.

BTW, it probably wasn't a good sign that while I was delivering miles to the broker's office there were two police officers there serving a summons for scalping event tickets. You can believe I cashed the broker's check immediately.