Can't be too hard for the cops to ask these idiots who they're selling to.
There you have it.
Illegal to sell or install a used cat in NY State where I worked, but sure it happens often enough. Not sure of the laws in other states.
I can't remember off hand ever replacing a stolen catalytic converter. Did plenty of exhaust work over the years.
BTW, there are very little quantities of precious metals (platinum and rhodium) in the average converter.
-Ken