Whoever has even once become notorious by base fraud, even if he speaks the truth, gains no belief.

Once someone is known to have deceived people, everything they say afterwards gets discounted, including the true parts. That is expensive and largely irreversible, because trust is not repaired by argument but by years of unremarkable evidence. The cost of a single serious deception is rarely counted properly at the time.

Guard this in yourself by refusing the convenient half-truth, even when it would smooth over a bad week. If you are deciding whether to believe someone with a history, ask for verification rather than assurances. Leave the door open to slow proof, since people can rebuild, just not quickly.