I should also clarify that I don't think that one needs a silver bullet argument of the type "the people who you would expect to be most trustworthy have the wrong belief on something that they've thought about, with very high probability" to conclude with high confidence that epistemic standards are generally very low.

I think that there are many weak arguments that respected authorities are very often wrong.

Vladimir M has made arguments of the type "there's fierce disagreement among experts at X about matters pertaining to X, so one knows that at least some of them are very wrong." I think that string theory is a good case study. There are very smart people who strongly advocate for string theory as a promising road for theoretical physics research, and other very smart people who strongly believe that the research program is misguided. If nothing else, one can tell that a lot of the actors involved are very overconfident (even if one doesn't know who they are).