Comment by vkou

Some states (Alabama, for instance, as I'm told by a contractor business operator friend who lives in it), requires you to either have a receipt from a licensed contractor who replaced whatever you're scrapping, or a business license to sell scrap copper.

I'm not wedded to any particular solution that will stop tweakers from getting cash from scrap yards no questions asked. Any mixture of them will work.

FWIW, I've asked him if the state mandating a 30 day delay on payments, or banning cash transactions for it would affect him any. His answer was 'not at all'.