My parents worked pretty hard to instill several important lessons in me. Some I picked up on better than others. One was that I should always try to be useful and always try to help other people. That was reinforced pretty heavily when I went to Boy Scouts or Sunday School. The message was pretty clear. You're here to have a positive impact on other people. It might be more important than anything else.
When I was much younger, one of the things that made me really uncomfortable and unhappy was that it was really common for people to make social, even romantic, connections with me just because they thought I could help with their job or some other financial aspect of their lives.
The end result was a situation where, whenever I met somebody, I'd wonder why they were there and if they really had any interest in me or were they just acting like it so I'd help them out. The times when that did become a problem, it was almost impossible to tell if somebody was genuine or not, and I made several mistakes when I trusted somebody who was not.
I don't know that I really blame them, though. In your twenties, life is kind of a survival game. Nobody is in a very stable situation, and taking a shortcut here and there can be very tempting, especially if your situation is really upside down and dire. I don't think anybody ever set out to hurt me. I think they just got desperate and saw me as a solution to their problem and didn't care enough not to hurt me.
It was particularly bad with people who struggled with addiction issues. With an addict, you're dealing with two people. One is normal and moral and usually really nice, and the other is an animal out to survive however it can, which sometimes meant me.