The hospital in this case is a middle man, and their role is vouching for the doctors they hire. When you buy a propane tank at Home Depot, the reason it doesn't blow up is that Home Depot's reputation depends on selling non-explodey propane tanks. When you buy meat at Whole Foods, why are you sure it's not rotten? Because the government checked that specific steak, or because you know Whole Foods wouldn't sell you rotten meat? Similarly, the reason people go to reputable hospitals is precisely because they know they can trust those places to hire competent staff.