I don't know what anyone else does with their convertors after the change them, but i took mine to work and these people come around and buy convertors, radiators, and other scrap. I made $80 on the factory one from my car, the replacement high flow only cost $40, so you can make money by replacing a cat

If you don't know anyone locally, you can get $50 if you send your old stock cat to Ed Morad. (Saw a post about this on 3800pro)