We should learn how to identify trustworthy experts. Is there some general way, or do you have to rely on specific rules for each category of knowledge?

Two examples of rules are never trust someone's advice about which specific stocks you should buy unless the advisor has material non-public information, and be extremely skeptical of statistical evidence presented in Women Studies' journals. Although both rules are probably true you obviously couldn't trust financial advisers or Women Studies' professors to give them to you.