> If I can give a small amount of help to someone in exchange for knowing if they are trustworthy or not, that's probably worth it.

That's a life skill I had to learn. I was raised believing that if I was a good altruistic person all that goodness would come back to me. Well, way too many times it didn't and it was extremely frustrating until I figured out how to deal with it.

Sometimes it's okay to be selfish. It stops people from taking advantage.