How We are Manipulated and What to Do About It.
David Maister in his article Can We Be Manipulated? discovers an unpleasant truth about manipulation.
Commenting on my one of my favourite books, Weapons of Fraud, he says
"Presumably, the theory behind the book is that, by being aware of the manipulative techniques that salespeople use, we will have better defenses. I'm not so sure. Note that these "tactics" are incredibly similar, if not completely identical, to how someone would behave if they really were trying to be helpful to you. Here's someone showing an interest in me, giving ideas away first to earn my trust, from an institution that I've heard of (the popularity or brand effect). That's what a REAL trusted advisor would do isn't it?" (my emphasis)
David then wonders how to determine real sincerity from fake. But the unpleasant truth remains: the techniques of manipulation are ethically neutral. Manipulators and schemers don't come to the social scene with a set of different tools of persuasion than those who are honest and reliable.
Thus, there is no simple due diligence trick with which to separate the foul from the fair. Certainly no maxim like "If it looks too be good to be true, it probably is." will work.
However, there is something in Weapons of Fraud that is useful - above and beyond the listing of a series of manipulative tricks. The authors introduce the notion of a "Phantom Dream", a state of affairs so desirable that you temporarily lose the ability to engage in skeptical thought. The general themes are health, wealth and death, how to obtain more of the first two, and avoid the third.
Even on the small chance it might be true, heaven is worth having and risking all for. (We have already seen this bad inference before, Pascal's wager.)
In Weapons of Fraud, the authors demonstrate how cunningly a skilled con criminal can detect and reinforce your Phantom Dream. Sometimes in a matter of minutes over the phone.
We may not be able to determine the sincerity of those who manipulate us: but we can resist the allure of Pascal's wager when we find its strange attraction working on us.

