How do you handle friends that are manipulative?

These people are pretty clever and it can take a while to realize that they are using you and manipulating you. I think they take advantage of the fact that you're likely to forgive your friends a lot of things that you might not put up with from somebody that you don't know too well. But once I realize that a so-called friend has been manipulating me, I end the friendship. Of course I try to talk to them about it first, and try to get them to understand what they're doing and that a relationship like that can't last, but I've never been successful in having them see it, or admit that what they're doing is wrong. Luckily, it hasn't happened to me many times, and sometimes it's hard to let the friendship go. But continuing it isn't worth the grief.

How do you know that they're really doing that to you? I mean, you can't really tell a person is being manipulative unless there's concrete proof. Your friend might just be doing this unconsciously. If it bothers you, talk to them and tell them how you feel.