What is the bias/thought process that results in distrust of "formal" knowledge in favor of "folk" knowledge?
This might be a matter of social proof; people generally absorb folk knowledge in a less-impersonal way than formal knowledge (your grandmother says it works, instead of hearing/reading that it might work from a reporter who read the abstract of the paper that says so).  I don't know if there has been formal work examining the role of social proof in the acceptance of folk knowledge, though.