Don't Believe Your Hype When a vendor compliments you on your savvy negotiation skills and offers you a once-in-a-lifetime, only-for-preferred-customers deal, rest assured that she'll be laughing at you all the way to the bank.

That's an example of what Robbins calls "mirroring"—using flattering statements to lift a listener's confidence in himself ("You're such a great judge of character!"). Confidence is, after all, where the con in con man comes from. The sharper someone makes you think you are, the more likely you are to believe that you're in control—and the more vulnerable you'll be when the loop of deception is closed. "The easiest person to con," says Robbins, "is someone who thinks he's too smart to be conned."

Walters agrees wholeheartedly, noting that "when we do interrogations, we find that in many cases, the more intelligent and confident the subject is, the easier it is, ironically, to take them down."

Figure Out the Incentives When all else fails, and you're really not sure whether someone's words should be trusted, Robbins suggests using the universal guideline behind understanding the dynamics of any business transaction: Follow the money. When you're trying to figure out if someone's deceiving you, it's critical to assess who wins and who loses if the proposition proves untrue, and by how much: Only pathological types will lie with no hope of gain, but the chance of an assertion gets bigger as the potential reward for lying rises and the consequences for being caught shrink. "Simply put, if someone has nothing to gain by telling a lie, chances are it's the truth," he says. "If it's obvious that he has something to gain, watch out."

This means being particularly skeptical of statements made by analysts whose firms may benefit from having them recommend certain stocks, for example, or C.E.O.'s trying to reassure investors to save their companies.

Walters agrees. "You look at the three major types of 'big' lies, which I call the Three H's: Hide, Hype, and Harm," he says. "People will lie to hide an indiscretion; people will lie to hype their own accomplishments; and people will lie to hurt someone or something that they want to exact vengeance on. All lies are ultimately motivated by gain, and the bigger the potential for gain, the bigger the lie."

And with the economy in its current state, both Robbins and Walters suggest exercising additional caution. Noting that statistics show spikes in bank fraud, personal-credit scams, and other financial misdeeds during downturns, Walters advises that businesses embrace Ronald Reagan's old line about nuclear arms treaties—"trust, but verify."

"In tough economic times, you have more and more people out there who are desperate," says Robbins. "Businesses and individuals get to a point where they already figure they're losing everything—they'll do and say things that they wouldn't do otherwise."

"It's a sad thing to say," Robbins adds, "but lying is a recession-proof business."