Some people do indeed stay quiet because they are trying to manipulate a situation in the background. Those are the ones you have to indeed watch out for. Judge them based strictly on their actions. But some quiet people are simply judicious with their words. No one ever listens to a person who talks a lot. Big talkers usually say a lot of words because they want attention or because they want to look smart.
Only speak when you have something important or insightful to say; people will listen to you and appreciate your words much more.
