Full Idea
Reliable testimony needs a good number of educated people, all of undoubted integrity, who have a lot to lose if they are caught lying, reporting very public events.
Gist of Idea
Good testimony needs education, integrity, motive and agreement
Source
report of David Hume (Enquiry Conc Human Understanding [1748], X.II.92) by PG - Db (ideas)
Book Reference
Hume,David: 'Enquiries Conc. Human Understanding, Morals', ed/tr. Selby-Bigge/Nidditch [OUP 1975], p.116
A Reaction
A nice checklist for flying saucer sightings etc: education, integrity, lying risky, very public. If any of those fail, it comes down to likelihood (apply Bayes?) and character assessment.