But that's not how it works, if you want anything more than old spark plugs and worn brake pads from the shop, you're going to have to pay for it, even if it's from your own car. It's called a cash on part exchange fee or something. The shops makes money off of scraping worn out/old parts too. If you want your old parts that have decent scrap value or can be refurbished, you have to pay up. Though there is a potential for profit if the amount of money you can make for selling the part directly to the scrap yard or refurbishing it is more than the fee.
But that's not how it works, if you want anything more than old spark plugs and worn brake pads from the shop, you're going to have to pay for it, even if it's from your own car. It's called a cash on part exchange fee or something. The shops makes money off of scraping worn out/old parts too. If you want your old parts that have decent scrap value or can be refurbished, you have to pay up. Though there is a potential for profit if the amount of money you can make for selling the part directly to the scrap yard or refurbishing it is more than the fee.
https://www.liveabout.com/core-charge-for-auto-parts-281542
That website explains it better than I can. I'd imagine the core fee on OEM catalytic converters is pretty high.