Edit: I forgot to address the OP...I'll be back!
When I confide in someone, disclose something very personal, I feel like a wounded animal in a corner, and there is some guy from animal control with a net slowly approaching. He wants to help me me, but I feel vulnerable and don't know what his motivation is and so I might growl at him or bite him, or try to escape. But a few people can convince me they mean no harm. When someone new is "bandaging me up", and they touch a tender part of my injury I might nip their hand, so to speak. But usually by the time I let you "work on me", I figure you didn't mean to do me any harm and it was an honest mistake. It takes a long time to get to that point though, and I don't know if I ever feel completely comfortable with it. If intimacy wasn't necessary I wouldn't dare risk it.
I have two groups of concerns when someone is urging me to trust them. My reaction to less familiar people is: Are their intentions immediately harmful? Why are they so interested in me? Are they wearing a wire? My reaction with familiar people is: Sure, they love you NOW, but what if they turn? What if they abandon you when they find out how worthless you are? What if YOU drive them away with your paranoia? They'll still have the dirt on you, and won't love you enough not to use it against you