Later, many people regretted doing this. Psychological manipulation can be a very powerful tool. So where does one draw the line. Even the thought of manipulating people can be repugnant to some. Others see the ends justifying the means.
Different people have different moral values on what is right and wrong.
So the place to draw the line would seem to differ from person to person. A person will face punishment for their manipulation if some persons involved discover a wrong that it has caused. The first guide in my mind of where to draw the line is where you cross the values of society as a whole. Now society is not uniform, but a person is generally aware of what is viewed as wrong by at least a significant portion of society. When a significant portion of society is offended, the issue makes the news, invites investigation, and for a business, results in a significant loss of employees or customers.