Another perspective of manipulative, is, the other person is incompetent or weak.
Pretty much, everyone is manipulative. Some just don't realize they're doing it, and most do it soo subtly, others don't realize it's happening. Very often, the subtlety has become a habit and a social norm. Take commercials ' guilt ' "destiny" ' and complements, for instance. They all, "secretly", cause you to do something in favour of the other person/organization. They didn't direct or ask you to do something; they've, just, made you feel a certain way and let you get to the conclusion they want.
The worst type of manipulation is when it's done out of fear of exile. The inknowledge of their own fears of exile; the inknowledge of their manipulation; the inknowledge of if they, actually, agree with what they're passing along. Bigots or Haters are, sometimes, examples of inknowledge manipulation. They will shame ' guilt ' and attempt conversion of others into their way, but their way is a direct response of "fitting in".
When people try to fit in, they will obscure themselves and their ideas (internally/personally) into pleasing others, so, others don't reject or abandon them. During this process, their manipulation is not "their own". As such, their manipulation can be considered as "not" manipulation, as it's not their will to begin with. However, because they are, still, manipulating, and they are inaware of their entirety, this form of manipulation is near-impossible to identify for either party, which makes it "the worst".
Under manipulation: as long as someone else does something they wouldn't normally do, and it's because they've communicated with you, you've manipilated them. It may take seconds... It may take years.
And, yes, there is such a thing as others legitimately-agreeing with you, and, that, can go either way, but convincement and influence is, just, another form of manipulation. The main difference, is, their realization and authentic desire to go a specific path because they've chosen to - under great consideration of information. (Not every path is a personal choice; some are followings... And some followings turn into leading, which obscure the origin of belief/not-what-i-wanted.)
