[cucumber3732842]

>You could also just require a license to scrap copper. That people can show up with a suspicious pile of metal and convert into cash seems to be what creates the opportunity for the thief.

So then they'll just sell to middle men.

And worse, in typical "what we need is a new law" fashion, you've taken a situation where one-ish person (the thief) has a financial incentive to see that the bad thing persists you now have two (the thief and the fence)

Also, electricians (the primary group who'd hold the licenses because they're scrapping a bunch of copper legitimately that stuff could be mixed into) already get enough undeserved make-work at society's expense as a result of their licenses. They don't need another side gig.