You put the Judiciary in charge of deciding the Truth, from the start the most trustworthy of the powers. Then, you only make it enforceable on stuff that fits a reasonably high standard of certainty. Then you subsidize its access to common people.
Putting the government in charge of deciding what is truth in advertising works on all kinds of countries. And works well.
Putting the government in charge of deciding what is truth in advertising works on all kinds of countries. And works well.