I don't think it's terrible at all. When I say manipulation, I mean something more sinister. It's hard to define, but it's something like using emotional tricks and playing games with people in order to try to exercise a great deal of control over them. Often the target isn't even aware what's going on, and if they were, they probably wouldn't agree to it.
What you're talking about seems very different from that. Everyone faces situations where it just isn't practical to be completely sincere or genuine. We all have to put up a bit of a front from time to time. I don't think there's anything wrong it, as to some extent it's just the grease that keeps the social machine moving smoothly. In fact, if you didn't do it, you'd be creating unnecessary friction that really serves no purpose. As long as it's done for good reasons, it's fine or even good.
Of course, it's definitely much better if it's give and take, with both sides doing their part to adapt to make things work. If two people work together and one is very talkative and social, and the other is quiet and keeps to themselves more, the quiet person needs to engage in a little conversation, and the talkative person needs to understand that the other person isn't always up for that.