I've been in the factories and supermarkets as a worker and an inspector. It's very rare (I don't say impossible, because there's always a chance) to find hair, sand, and other foreign objects in meat processed in registered factories - the cleanliness is pretty high up there because the fines are also high up there.

But if you're getting meat from an unregistered butcher/retailer, you're on your own. You can also see/inspect the meat in the display case before you buy.