The study of history reduces to two tasks. One: reading primary sources. Two: assessing their credibility. If we know whom in the past to trust, we know the story of the past. Until he makes this judgment, the historian is no more than a database administratorI disagree. We should assume that there is no more than moderate credibility anywhere, regardless if someone is right a few times. In general fields are narrow, and the default is that experts will be magnificent in their field, and near-worthless outside it. Einstein, for instance, revolutionized physics...and then proceeded to insist that "God does not play dice with the universe", rejecting notable parts of the next paradigm.
People are wrong a lot, and there are NO historical sources that you can TRUST. Just as there are no governments you can TRUST.
One more time...it's all Bayes, all the way down.