Things are happening on more levels than just pure body language. I think you’ll find the body language is secondary to the main body of communication. For example, nodding at each other whilst saying how bad the service is at the local supermarket, the conversation being profoundly negative, however strong positive messages are causing bonds to be formed. However, have you ever had the case where you go along with things, agreeing, nodding, bemoaning, only to walk away relieved that the ordeal is over. It is amazing how easily we mimic, we can slip in and out of this behaviour without noticing. Interestingly these behaviours are generally lacking high functioning autistic spectrum people. One interesting question, are mild autistic people perceived as socially challenged because they lack these traits or do they lack these traits because of being socially challenged. Unfortunately for high functioning autistics the answer doesn’t help them, only the people who occasionally get a dose of truth from them.

Another point; if you were to nod in agreement, mimic and so on, but never make eye contact, or worse, distinctly look to one side, or up into the middle of your fellows forehead, the mimickery effect would be destroyed. All messages have to be congruent and we are acutely aware when they’re not. People refer to this as instinct. Being nervous can thwart your normal behaviour and send mixed messages. Also most video conference facilities for people to look at a screen, whilst the camera is elsewhere, can actually cause distrust (search for the MIT paper on this subject). I would argue that eye contact is probably more important than mimicking.

An interesting study I’d like to do one day to collect empirical evidence (excuse to go out drinking) is how body language can communicate across a larger distance. Identify people in a bar that are perhaps interested in each other, or conversely, perhaps competing with each other. They’re body language synch’s up, despite being quite far apart and perhaps not consciously aware of each other. Taking this a step further you can actually mimic someone across a room and the results can be quite freaky if you’re the sort of person that likes to play such games, especially when alcohol is involved. Other examples are where groups identify with each other through posture, gesture and how they adorn themselves. This can be spotted from great distances and is fundamental to society.

Usually, you won’t be able to change your status by consciously choosing to mimic or not. But, if you could, you would rarely want to signal your willingness to be the follower if you aren’t already.

Basically, if non-mimics are more skeptical, they’ll catch lies more but catch truths less. Vice-versa for mimics.

Even if people do lie somewhat often, “Mimics better understand what we’re trying to communicate” may be a much better explanation of why we like them than “Mimics believe any old lie we tell them!”

(I know there’s a sizable literature on imitation, including things like “mirror neurons,” but I am entirely ignorant of that literature. There is also a large literature on things like kin altruism and reciprocity, and I’m almost entirely ignorant of that literature too. So quite possibly I’m dreaming up scientifically impossible examples here, beware.)

E.g., animals might respond favorably to mimicry because it spoofs a heuristic (“he is behaving more similarly to me than most members of my species, therefore he has probably inherited more of the traits I carry”) for kin altruism. Or “he is mimicking me, and for much of my evolutionary heritage that has been a strong indicator that we were attentively learning useful behaviors from each other, and so I reduce my estimate of the probability that he’s trying to sneak up on me merely to steal my food.”