You should not try to sell your American Airlines vouchers. This is why
Attention all American Airlines passengers: If you have any flight vouchers stored away somewhere, don’t try to sell them. If you do, the airline might use high-tech security systems to catch you.
If you try it and American Airlines finds out, it will mark your vouchers stolen, leaving you with nothing.
This tale is a cautionary one for anyone considering skirting the terms of their American Airlines vouchers. There are many hacks out there advising travelers about how to make a profit on these bonuses. But much of that “guidance” overlooks an undeniable obstacle: almost every airline forbids this practice, and offering your vouchers for sale can cause them to become instantly worthless.