This reminds me of how historians trying to find out about the historical Jesus have come up with some (objective?) criteria about what to accept as true.

Examples:

* Multiple attestation. Do we have multiple independent sources telling us the same thing?

* Contextual credibility. Do people behave in a way that's plausible given their setting (the languages they spoke, what they knew at the time).

* Embarrassment. Is this detail actually inconvenient for the person relaying it (and not the sort of thing they'd make up)?

see "Criteria of authenticity" in https://en.wikipedia.org/wiki/Quest_for_the_historical_Jesus