You've got a cat in a box. It was killed or not based on the outcome of a fair coin flip. Your prior for the cat being alive should be 50%. If you hear meowing and your prior stays at 50%, you are not very good at applying logic to contrived scenarios.
We have a complex financial transaction in a black box. My prior on there being a technical fudging on at least one term of it is, hmm, maybe 5%. If you tell me "A reputable observer says there was no impropriety", that goes down. If you tell me "A socialist says, while fulminating about imperialists, that there was no impropriety", my new estimate is high-nineties.
The box is meowing, loudly.
(slight quibble about your example: a fulminating socialist could just as well make that statement in the absence of impropriety. the additional information that that's the best possible report would indeed make it sound like a meow.)