I like to think I'm a good judge of character, but I've been proved wrong so many times that I no longer trust myself.
For example, there was an elderly guy who lived on our estate with his wife. He was a lovely old school Londoner, very gentlemanly and polite. I later learned that he'd been a violent criminal in his youth and had spent 12 years in prison for robbing banks and security vans! (Still couldn't help liking him.)