If you're duplicitous, disingenuous or otherwise manipulative towards another person, then consider the mistake you're making. By being manipulative, you're counting on a weakness or foolishness in the person whose behavior you seek to alter by a means other than reason. You're doing this -- why, exactly? You're doing it in order to gain something from them. What are you trying to gain? Something involving their intelligence or sophistication. In practice, you're counting on someone to be weak and foolish so that you can utilize their intelligence and wisdom.

Don't you think if a person really is worth manipulating, he's likewise incapable of being manipulated?

The contradiction involved is obvious. That's why only the foolish and unintelligent are stupid enough to practice deception or manipulation. They're right that they need assistance. But they're not going to get it in this way -- at least, not from anyone who has something to offer.