A private company (or multiple, given the free market competition) transparently releases information to the public about restaurants that associate with them (And why wouldn't they if they wanted to lure customers that prefer a clean environment?) via privatized certifications based on standards upheld by said company.

If a customer doesn't see the certification on the wall, or disagrees with the requirements/standards of the certification then they are free to chose another eating establishment to patron.

Seems easy enough.