People are so easy to swindle because the swindler has as accomplices the victim's own moral defects. When good judgment and moral sense are suborned by lust or greed or sloth or vanity or anger, the one swindled participates willingly in his own undoing. In the end he swindles himself.
How is it, for example, that Bernie Madoff 'made off' with so much loot? You have otherwise intelligent people who are lazy, greedy and vain: too lazy to do their own research and exercise due diligence, too greedy to be satisfied with the going rate of return, and too vain to think that anything bad can happen to such high-placed and sophisticated investors as themselves.
Or take the Enron employees. They invested their 401 K money in the very firm that that paid their salaries! Now how stupid is that? But they weren't stupid; they stupefied themselves by allowing the subornation of their good sense by their vices.
The older I get the more I appreciate that our problems, most of them and at bottom, are moral in nature. Why, for example, are we and our government in dangerous debt? A lack of money? No, a lack of virtue. People cannot curtail desire, defer gratification, be satisfied with what they have, control their lower natures, pursue truly choice-worthy ends.