Identify manipulative behaviors. Manipulators are very good at what they do: controlling others. Their tactics vary, but the goal is always to get the manipulated to do what the manipulator wants. Manipulative behaviors can include threatening, flattering, giving you guilt or demeaning you. They may keep you guessing by alternating between excesses of affection and charm and coldness or anger. If you often feel stressed and resentful when dealing with someone, you may be enmeshed in a manipulative relationship.
Look at ways in which you play into the manipulator's hands. List things you have done or not done to please the manipulator and how you felt when at the time.
Figure out which buttons the manipulator is pressing. For example, if you are a giving and caring person, a manipulator might suggest that you are cold and selfish if you are start resisting the manipulator's schemes.
Stop making excuses for the manipulator. If you blame the manipulative behavior on his insecurities or unhappy childhood, know that such excuses are a key part of his manipulative strategy. Be wary of anyone who regularly "plays the victim."
Turn down "generous" offers of help, money, time, etc. To a manipulator, these are always "quid pro quo." Manipulators use "gifts" they give to get something out of you.
Assert yourself. Say no to manipulative demands calmly and rationally.
Establish and maintain boundaries. You need to distance yourself emotionally in order to deal with the manipulative comments and behaviors. Cultivate detachment and consider it necessary "tough love."
Challenge lies and half-truths. Use logic instead of emotion to argue back. If necessary, end the battle by "agreeing to disagree." Hold your position. Be prepared to repeat yourself many times until the manipulator backs off.
Prepare yourself for the manipulator to escalate her behavior. The manipulator will not give up control without a fight. You will hear how "mean" you are and how "hurt" she is by your "uncaring" behavior. The manipulator's behavior may become worse than ever or she may totally withdraw. Stand firm, don't get defensive and don't take the bait.
See how the manipulator responds to the changes you have made. Some people see the error of their ways and come to appreciate the benefits of a more equitable relationship. Once you deal with the manipulator, you will feel more optimistic, more powerful and once again in control of your destiny.
And, after reviewing a few other notes on the subject, also avoid saying "I'm sorry...", instead say things like "It's a shame you feel that way, but here's what I am available to do". Also, remember to say "I'll get back to you" and "Let me think about it", so you can get away from the distorted situation and think clearly about what you are willing to do.
Remember, manipulators have often been manipulated and feel this is the only way to get ahead...always recognize they are unhealthy but pray for them.