We deliver some of our corn to a large milling plant. They make several products from the corn and their customers are world wide. They randomly test loads for various things. This way they can assure their clients that they have an ongoing testing plan. The funny thing is that if two trucks from the same farmer or small elevator enter together,(obviously loaded simultaneously back home) they might randomly test the first one, reject it for some reason, and not check the second truck for the same offense, because it's not time for another random check.
It would seem that they may not be trying very hard to find offenders. But at least in this manner they can assure consumers that they are being vigilant.
I see Major League Baseball has implemented a similar testing program.