Regarding your bible comment, why would you not toss the entire thing out if you find some parts are not believable/true?…If some aren't true then how do you know any are true?
No, because not all claims are dependent on the truth of other claims.
I have a mechanic who believes the Covid virus has microchips in it planted there by Bill Gates. He is paranoid, ill informed about politics, and allows his perception of facts to be twisted by ideology. In this subject matter, he's not credible.
He also thinks that the rotors on my brakes are worn out because he's seen it a thousand times before and has physical evidence it's happening with my car, now. His job depends on good diagnoses, he has training in the relevant area, and he has evidence.
I have no problem accepting the second claim regardless of the first.