My experience has been that if you sit down and are honest and decent with 4 people, one of those 4 will try to take advanage of you. Being decent and nice guaranttees you will fight with those who aren't. Being a good man on a street with drug pushers mean you will end up fighting.
It takes tough people to be decent and honest. They must fight for it. When you find the Ted Bundies you go after them and stop them. Honesty and decency reguire that you be willing to fight for it. It is a costly affair.
FYI I try to spot the lairs, Bundy's, with consistency. They say something inconsistent (Not Fool Proof. God always get it right. Me, not so often.) I was with a rapist as few hours before he tried to rape a girl. Sitting in a car, he said something out of the clear blue which made no sense to me, about the girl who was going to try to rape that night. Ever since, whenever I hear non sequitors, I focus my full attention on that person.
Second, experience helps alot. Guys who are capable of murder do have a different feel about them. Unfortunately, experience is a painful quantity to aquire. Frequently requiring you to look like an ass first.