Here's an interesting article on some fascinating aspects of human behavior and neurology where persuasion is involved...
http://tinyurl.com/thxjv
So, people seem to want to have their sense of fairness satisfied during a transaction, even if they have nothing to gain and everything to lose otherwise. And I think that we've all observed this in action at one time or another in our lives.
The rest of the article is interesting and I think the author makes some conclusions in the last two paragraphs which I don't know match my experience. And maybe that's for the best!
Be Well,
Michael Perez