Generally common sense, good wisdom, and my own understanding of the situation as well as my personal investigation.

Like everything I need to know about nutrition is "eat food, but not too much, try and get a variety, generally plants are better for you than sugar, fast regularly and get exercise."

I've personally be satisfied with what I'll call "informed" common sense. An example from health is the documentary "In Defense of Food" where the journalist uses a little science and history to create the heuristic: "Eat food, mostly plants, not too much." None of those insights are really surprising, the only exception maybe being the "mostly plants part".

A downside of depending on complicated theories from experts is that it makes a "priesthood" of people telling you what to think all the time. I think there are enough examples from health, environmental, and privacy policy making to demonstrate that the "priests" don't always have the public's best interests in mind.

Most people end up trusting their family historical wisdom.

Whoever sells the most books.