Supervision generally involves a full-time employee trained in the laws of kashrut, supplemented by outside inspectors who make surprise visits on a regular basis. If you want to know whether a business has supervision, you can ask to see its certificate, which is usually on display. Obviously, this system works only if consumers can safely assume that such certificates are genuine. Even with a prohibition on fraud, the system of private supervision is not perfect. It relies, to a considerable degree, on trust.
Consumers trust the mashgichim, and the mashgichim, to some extent, trust business owners.
This trust is based largely on shared religious values. But both mashgichim and the businesses they supervise have to worry about maintaining their reputations in the face of competition, which is not true of state inspectors. An establishment that has been known to mislead its customers will not stay in business long, and a mashgiach who is known for corruption or carelessness can no longer practice his occupation. At first glance, the New Jersey and Maryland cases seem to suggest a need for state supervision. But County Kosher is also under the private supervision of another Orthodox rabbi, who insists that the state inspector is mistaken.