Grey psychology is like a weapon. When it is the hands of a surgeon it cures else kills.
These are tricks to exploit weakness of human mind. Our mind is very predictable. We can easily manipulate behavior of people to our favoring. Advertisers,actors,politicians,seducers,players,media,businessmen, they all do it.
It is not always bad. If you use some tricks to get the girl you really love,its fine. But if you use it to emotionally destroy 22 girls and use them for sex , its bad and unhealthy.
One thing for sure,it works all the time!