Insincerity is saying what one believes another person wants to hear. It is a power behavior because it is meant to disarm the other person from their options of critical thinking, or acting promptly on a boundary. It is possible to say something insincerely that is actually true, and also possible to say insincerely something with which one does not disagree. All lies are insincere, but not all insincere statements are lies. A mistake is a statement that while untrue, is delivered sincerely.
Most insincerity becomes obvious as actions fail to match up with statements and promises. However, insincerity can be recognized immediately as a conversation goes on by reversals, internal contradictions, and especially the over-inclusion and parrotting of ideas and words the target person has just been using. Other signs are over-the-top compliments and a forced familiarity. Also the voice will give an indication, as with other parts of the 'con.'
A common controlling maneuver is to deliver a mix of many true statements and a few lies. This is sometimes called a 'mindf*ck.' The difficulty for the survivor, is that going along or resisting, based on the feeling of truth or falsity of what is said, is much more difficult because of the mixture. However, if the insincerity is detected, the overall controlling intention becomes easily evident.