Just as you shouldn’t take positive correlation to be proof, you also shouldn’t take negative correlation to be an automatic dismissal.
Someone can be trying to take advantage of you, but using true information to do so. Lying and manipulating aren’t positively correlated with things that are advantageous to you, but that doesn’t mean that every word out of someone’s mouth is false just because some things were.
This makes the world more complicated than most people would like it to be – it would be nice if all lies came from “liars” and all liars always lied, like doors in a riddle. But they don’t.
So you can’t just outsource all of your decision-making onto external people you’ve categorized as “good” or “bad.” Doing everything that a given person tells you to do is a recipe for disaster, but so is deliberately doing the opposite every single time out of spite. In both cases, that person is controlling you and you’ve yielded all agency.