Here in California scales and any device used in weighing "sold" items has to be checked and verified by county on regular schedule. They also do random spot checks of all businesses that utilize a weights and measures type of sale. So all bins, cans and dumpsters that are part of the weighing system are serial numbered and usually have the tare weights posted near the scale or in the office. If weights and measures inspectors find a businesses that is fraudulently conducting their businesses they can and do shut them down.

That is the rules, but with all government operation they are stretched way to thin and can't possibly get to all the places they need to. Ironically it is the department of agriculture that weights and measures division comes under. So can only wonder how much a agriculture bureaucrat knows about a scrap yard operation. I do know of one yard that was shut down for scale fraud, they close for about a month and opened under "new management". Everyone there looks to be same workers, so who knows?