Can't sell a used cat here. Maybe some unscrupulous yards might buy them? No idea what they do with them.
I can get Cat's all day long from salvage yards in SoCal, it's who you know...
Walmart will give $12.00 last time I bought a battery, any battery seller will buy cores for that price, some will buy good condition batteries for a bit more when they look like they are new and they load test good.
They gut the cat, the honeycomb ceramic is then broken down and the platinum, palladium, and rhodium are extracted. The thieves are at the bottom of the the pyramid. These are organized groups with equipment and knowledge to extract the materials.
Ding, ding, winner. This is the most profitable way, and the person that performs these precious metals recovery operations is the person that makes the money, not the thief!
P.S. There is Rhodium in a cat? I think Rhodium is the most expensive metal I know of. I doubt but a couple people here may know what its main use is for.