When Harpending reached San Francisco, there was an excitement in the air recalling the Gold Rush days of the late 1840s. Two crusty prospectors named Philip Arnold and John Slack had been the ones to find the diamond mine. They had not divulged its location, in Wyoming, but had led a highly respected mining expert to it several weeks back, taking a circular route so he could not guess his whereabouts. Once there, the expert had watched as the miners dug up diamonds. Back in San Francisco the expert had taken the gems to various jewelers, one of whom had estimated their worth at $1.5 million.

Harpending and Ralston now asked Arnold and Slack to accompany them back to New York, where the jeweler Charles Tiffany would verify the original estimates. The prospectors responded uneasily—they smelled a trap: How could they trust these city slickers? What if Tiffany and the financiers managed to steal the whole mine out from under them? Ralston tried to allay their fears by giving them $100,000 and placing another $300,000 in escrow for them. If the deal went through, they would be paid an additional $300,000. The miners agreed.

The little group traveled to New York, where a meeting was held at the mansion of Samuel L. Barlow. The cream of the city’s aristocracy was in attendance—General George Brinton McClellan, commander of the Union forces in the Civil War; General Benjamin Butler; Horace Greeley, editor of the newspaper the New York Tribune; Harpending; Ralston; and Tiffany. Only Slack and Arnold were missing—as tourists in the city, they had decided to go sight-seeing.

When Tiffany announced that the gems were real and worth a fortune, the financiers could barely control their excitement. They wired Rothschild and other tycoons to tell them about the diamond mine and inviting them to share in the investment. At the same time, they also told the prospectors that they wanted one more test: They insisted that a mining expert of their choosing accompany Slack and Arnold to the site to verify its wealth. The prospectors reluctantly agreed. In the meantime, they said, they had to return to San Francisco. The jewels that Tiffany had examined they left with Harpending for safekeeping.

Several weeks later, a man named Louis Janin, the best mining expert in the country, met the prospectors in San Francisco. Janin was a born skeptic who was determined to make sure that the mine was not a fraud. Accompanying Janin were Harpending, and several other interested financiers. As with the previous expert, the prospectors led the team through a complex series of canyons, completely confusing them as to their whereabouts. Arriving at the site, the financiers watched in amazement as Janin dug the area up, leveling anthills, turning over boulders, and finding emeralds, rubies, sapphires, and most of all diamonds. The dig lasted eight days, and by the end, Janin was convinced: He told the investors that they now possessed the richest field in mining history. “With a hundred men and proper machinery,” he told them, “I would guarantee to send out one million dollars in diamonds every thirty days.”

Returning to San Francisco a few days later, Ralston, Harpending, and company acted fast to form a $10 million corporation of private investors. First, however, they had to get rid of Arnold and Slack. That meant hiding their excitement—they certainly did not want to reveal the field’s real value. So they played possum. Who knows if Janin is right, they told the prospectors, the mine may not be as rich as we think. This just made the prospectors angry. Trying a different tactic, the financiers told the two men that if they insisted on having shares in the mine, they would end up being fleeced by the unscrupulous tycoons and investors who would run the corporation ; better, they said, to take the $700,000 already offered—an enormous sum at the time—and put their greed aside. This the prospectors seemed to understand, and they finally agreed to take the money, in return signing the rights to the site over to the financiers, and leaving maps to it.

News of the mine spread like wildfire. Prospectors fanned out across Wyoming. Meanwhile Harpending and group began spending the millions they had collected from their investors, buying equipment, hiring the best men in the business, and furnishing luxurious offices in New York and San Francisco.

A few weeks later, on their first trip back to the site, they learned the hard truth: Not a single diamond or ruby was to be found. It was all a fake. They were ruined. Harpending had unwittingly lured the richest men in the world into the biggest scam of the century.

The logistics of the con were quite simple. Months before Arnold and Slack announced the “discovery” of the diamond mine, they traveled to Europe, where they purchased some real gems for around $12,000 (part of the money they had saved from their days as gold miners). They then salted the “mine” with these gems, which the first expert dug up and brought to San Francisco. The jewelers who had appraised these stones, including Tiffany himself, had gotten caught up in the fever and had grossly overestimated their value. Then Ralston gave the prospectors $100,000 as security, and immediately after their trip to New York they simply went to Amsterdam, where they bought sacks of uncut gems, before returning to San Francisco. The second time they salted the mine, there were many more jewels to be found.

The effectiveness of the scheme, however, rested not on tricks like these but on the fact that Arnold and Slack played their parts to perfection. On their trip to New York, where they mingled with millionaires and tycoons, they played up their clodhopper image, wearing pants and coats a size or two too small and acting incredulous at everything they saw in the big city. No one believed that these country simpletons could possibly be conning the most devious, unscrupulous financiers of the time. And once Harpending, Ralston, and even Rothschild accepted the mine’s existence, anyone who doubted it was questioning the intelligence of the world’s most successful businessmen.

In the end, Harpending’s reputation was ruined and he never recovered; Rothschild learned his lesson and never fell for another con; Slack took his money and disappeared from view, never to be found. Arnold simply went home to Kentucky. After all, his sale of his mining rights had been legitimate; the buyers had taken the best advice, and if the mine had run out of diamonds, that was their problem. Arnold used the money to greatly enlarge his farm and open up a bank of his own.

Given how important the idea of intelligence is to most people’s vanity, it is critical never inadvertently to insult or impugn a person’s brain power. That is an unforgivable sin. But if you can make this iron rule work for you, it opens up all sorts of avenues of deception. Subliminally reassure people that they are more intelligent than you are, or even that you are a bit of a moron, and you can run rings around them. The feeling of intellectual superiority you give them will disarm their suspicion-muscles.

In 1865 the Prussian councillor Otto von Bismarck wanted Austria to sign a certain treaty. The treaty was totally in the interests of Prussia and against the interests of Austria, and Bismarck would have to strategize to get the Austrians to agree to it. But the Austrian negotiator, Count Blome, was an avid cardplayer. His particular game was quinze, and he often said that he could judge a man’s character by the way he played quinze. Bismarck knew of this saying of Blome’s.

The night before the negotiations were to begin, Bismarck innocently engaged Blome in a game of quinze. The Prussian would later write, “That was the very last time I ever played quinze. I played so recklessly that everyone was astonished. I lost several thousand talers [the currency of the time], but I succeeded in fooling [Blome], for he believed me to be more venturesome than I am and I gave way.” Besides appearing reckless, Bismarck also played the witless fool, saying ridiculous things and bumbling about with a surplus of nervous energy.

All this made Blome feel he had gathered valuable information. He knew that Bismarck was aggressive—the Prussian already had that reputation, and the way he played had confirmed it. And aggressive men, Blome knew, can be foolish and rash. Accordingly, when the time came to sign the treaty, Blome thought he had the advantage. A heedless fool like Bismarck, he thought, is incapable of cold-blooded calculation and deception, so he only glanced at the treaty before signing it—he failed to read the fine print. As soon as the ink was dry, a joyous Bismarck exclaimed in his face, “Well, I could never have believed that I should find an Austrian diplomat willing to sign that document!”

The Chinese have a phrase, “Masquerading as a swine to kill the tiger.” This refers to an ancient hunting technique in which the hunter clothes himself in the hide and snout of a pig, and mimics its grunting. The mighty tiger thinks a pig is coming his way, and lets it get close, savoring the prospect of an easy meal. But it is the hunter who has the last laugh.

Masquerading as a swine works wonders on those who, like tigers, are arrogant and overconfident: The easier they think it is to prey on you, the more easily you can turn the tables. This trick is also useful if you are ambitious yet find yourself low in the hierarchy: Appearing less intelligent than you are, even a bit of a fool, is the perfect disguise. Look like a harmless pig and no one will believe you harbor dangerous ambitions. They may even promote you since you seem so likable, and subservient. Claudius before he became emperor of Rome, and the prince of France who later became Louis XIII, used this tactic when those above them suspected they might have designs on the throne. By playing the fool as young men, they were left alone. When the time came for them to strike, and to act with vigor and decisiveness, they caught everyone off-guard.

Intelligence is the obvious quality to downplay, but why stop there? Taste and sophistication rank close to intelligence on the vanity scale; make people feel they are more sophisticated than you are and their guard will come down. As Arnold and Slack knew, an air of complete naivete can work wonders. Those fancy financiers were laughing at them behind their backs, but who laughed loudest in the end? In general, then, always make people believe they are smarter and more sophisticated than you are. They will keep you around because you make them feel better about themselves, and the longer you are around, the more opportunities you will have to deceive them.

There is, however, one situation where it pays to do the opposite—when you can cover up a deception with a show of intelligence. In matters of smarts as in most things, appearances are what count. If you seem to have authority and knowledge, people will believe what you say. This can be very useful in getting you out of a scrape.

The art dealer Joseph Duveen was once attending a soiree at the New York home of a tycoon to whom he had recently sold a Dürer painting for a high price. Among the guests was a young French art critic who seemed extremely knowledgeable and confident. Wanting to impress this man, the tycoon’s daughter showed him the Dürer, which had not yet been hung. The critic studied it for a time, then finally said, “You know, I don’t think this Dürer is right.” He followed the young woman as she hurried to tell her father what he had said, and listened as the magnate, deeply unsettled, turned to Duveen for reassurance. Duveen just laughed. “How very amusing,” he said. “Do you realize, young man, that at least twenty other art experts here and in Europe have been taken in too, and have said that painting isn’t genuine? And now you’ve made the same mistake.” His confident tone and air of authority intimidated the Frenchman, who apologized for his mistake.

Duveen knew that the art market was flooded with fakes, and that many paintings had been falsely ascribed to old masters. He tried his best to distinguish the real from the fake, but in his zeal to sell he often overplayed a work’s authenticity. What mattered to him was that the buyer believed he had bought a Dürer, and that Duveen himself convinced everyone of his “expertness” through his air of irreproachable authority. Thus, it is important to be able to play the professor when necessary and never impose such an attitude for its own sake.