I think it's hard to tell the difference. I myself often cry because I am very emotional. I can cry if I saw any heartbreaking post on the network, but at the same time I'll leave in a minute and as if nothing had happened. At the same time, I will not writhe, make sounds. Just a classic tear will flow and it seems like he has already cried, sincerely. As a rule, now people play for the camera: they kill themselves, shake, yell in a voice that is not their own. Because it has become a canon of behavior when you are upset. Everyone will pay attention to this, because the "actor" wants it himself.
My friend was in a stressful situation, with me she held back (we live together), but one day she locked herself in the bathroom, turned on all the taps and cried. This could only be heard if you listened, I listened, because I was worried about her. At the same time, she went out and there was a smile on her face, as if she had not cried at all.
It seems that the sincerity of tears can be determined only by feeling the person. If he is a well-known manipulator, if you know that there may be some kind of emotional trick, then the ANSWER is obvious - this is a theatrical performance, but if you feel that things are really bad and the person is really unstuck - support, do not stand aside ! :)
I am adding: water from the nose flows like a river of plakunov (checked on myself!)
Referring to what I read from Paul Ekman, and what I observed in life, crying and sad people have wrinkles in a certain shape on their foreheads, and it is almost impossible to fake these wrinkles if you are not an actor. It looks like this: the inner corners of the eyebrows rise up and come closer to each other, sometimes the wrinkles between the eyebrows can resemble a horseshoe (but this is individual). This is the most basic thing, well, the rest is rapid breathing, blush, the lower lip tucked towards the top and stretched to the sides (there are also wrinkles on the chin), obvious tears. In general, it still depends on the strength of the emotions at which crying occurs and how intense it is, plus it can take partial forms, such as the eyebrows are involved, but the lips are not.
Completely all parts of the face in the cry can be it is good to see in children, as they usually do not yet know how to mask emotions:
Tears are flowing in a stream, the face turns purple, the lips are distorted with an extended grimace, which, by the free will of the crying one, cannot pass. The lips will shake, the chin will tremble.
In general, sometimes it is obvious to distinguish when crying sincerely and when not.
Very often crying people turn away, put their heads up, freeze in one position, because crying is a very stressful situation for the body, the body does not have the strength for other actions. The crying person can choke on his own saliva, mucus runs from the nose.
Usually, the one who cries insincerely, very quickly and easily calms down, easily switches to another topic of conversation. A person who is really genuinely upset and crying cannot be so flexible in changing his mood, I think. Although it can happen in different ways for everyone :)