Sometimes trusting people can be hard to manage, but being kind is never a mistake.
Smiles, being positive, and trying to get others to talk about themselves instead of talking about you seems to make people more honest and vulnerable. For example, instead of saying "Sorry" say "Thank you." "Sorry I'm late" becomes "Thank you for waiting for me." Of course, it's also important that we relate to others in a healthy way. The ones who love and respect you back are the ones who stay and should stay for that matter. If someone doesn't want to be your friend, they don't have to. And if you believe people are trying to take advantage of you, you are free to move on to people who you enjoy more.
Just some thoughts!