In philosophy, the Principle of Charity is a technique in which you evaluate your opponent’s position as if it made the most amount of sense possible given the wording of the argument. That is, if you could interpret your opponent's argument in multiple ways, you would go for the most reasonable version.
There is a corollary to the Principle of Charity which I'm calling Bayesian Charity. It says that, in general, you should interpret your opponent's wording to be advocating the most popular position.
This is implied by Bayes Theorem. Your prior for whether someone believes something unpopular should be related to its popularity. Since an unpopular belief, by definition, has few believers, your prior for whether someone believes an unpopular position should be lower the less popular the position is, and you should update your prior based on how clear their statement was.
Extraordinary claims require extraordinary evidence. If someone said something to me suggesting that the moon landing was real, I wouldn't think twice about it. Most people believe the moon landing was real. However, if someone said something suggesting that the US has an underground base on Mars, I'm going to ask for clarification.
Context matters, of course. If you're at a flat Earther convention, your prior should be much higher that any random person believes in a flat Earth. But in general, if someone says something that almost no one believes, it's probably a good idea to confirm you understood what they meant before assuming they hold such a fringe opinion.