If you're referring to gullability I think we're all capable of falling for something if taken off guard or it's from someone you've trusted.
The thing is to learn from each experience. I like to believe that most people are genuine and if you don't have a certain amount of trust you'd never get anywhere or have any friends.
Having said that I tend to take little at face value immediately these days, which makes me a cynical old bastard
As for more extreme brainwashing, as in weird cults or theories and the like, then not at all. Like John above, I'm far too opinionated and would need more convincing and proof than most would be able to give. You see so many jumping on these bandwagons about things instead of taking time to analyse all angles.