AC Evacuation and Resale

I know there are a few people on here that are set up to evacuate their own freon and they make more business by charging other people to do it as well. My question is do you then turn around and sell the refridgerent to other hvac companys or customers. I know you need a special license to recover it but do you need one to resell it if there is a market? Could you sell it to auto shops for cars, especially if you are set up to recieve r-12.