Sophia looked unkempt and arrived at the East Hampton, New York, mansion in an old van with her two kids. They say hindsight is 20/20, and, looking back, Susan McGraw, a senior vice president at the Corcoran Group, sees the signs her so-called buyer was an impostor.

At the time, however, McGraw suppressed her doubts. After all, Sophia was a referral from a respected colleague. And, McGraw points out, “I’ve had people like that before—you don’t think they have any money at all, but sure enough, they’re real.

Claiming she was about to receive a windfall from a major European deal, Sophia stepped inside the brand-new, $3.5 million house and made a full-price offer. The children raced upstairs and selected their bedrooms. A contract was drawn up. McGraw managed to contact Sophia’s lawyer by phone about faxing over documents, and that’s when she started to question the buyer’s legitimacy.

“I found it odd that a woman who had millions and millions of dollars in assets should have an attorney whose fax machine would run out of paper,” McGraw says.

As time passed and Sophie’s excuses not to sign the contract piled up, cracks appeared in her story. After a little digging, McGraw discovered that this supposedly wealthy woman was living in a two-family house in Queens. Eventually, Sophia vanished.

“You get drawn in,” McGraw explains. “Like any good con artist, they always have an answer. You start doubting yourself: Are you being paranoid? Should you give this person a chance? Then you realize this person is taking you for a ride.”

In the upper reaches of the real estate market, impostors like Sophia are an increasingly common problem. These people aren’t just voyeurs who don smart outfits and attend open houses for places that are out of their reach. When it comes to multimillion-dollar properties, the showings are often private—and wannabes will do just about anything to get inside, from concocting elaborate stories of wealth to assuming false identities. Often, the fake buyers are relatively benign, simply wasting a broker’s time in order to feel rich and be catered to. In other cases, they are true con artists out to scam money, identities, or even a house.

In part, such behavior can be attributed to the public’s increasing fascination with riches. “In the U.S. there’s a cultural promise of prosperity,” says Paul Schervish, director of the Center on Wealth and Philanthropy at Boston College. “You’re not going to gain prosperity through royalty; here, common people can become financial royals. And if you can’t become one, you can pretend to be one for a while.

“It’s like a sophisticated amusement park,” he says. “It’s visiting Wealth Land.”

The presence of high-end real estate listings on the internet has also fueled the phenomenon. “These properties have more global presence now,” says Shari Chase, president and C.E.O. of Chase International, a real estate firm in Lake Tahoe, Nevada. “There’s a lot more ability today to do research than there has been. For people with nothing better to do, this is a great pastime.”

As a result, prequalification, which requires a broker to review financial documents to ensure that a person has the means to buy a property, is becoming the norm. And agents who handle luxury listings increasingly know to ask personal questions (such as “where do you live?”) before showing a home. And yet, despite heightened vigilance, scammers slip through the cracks.

In his 11 years as a Los Angeles-based broker, Mauricio Umansky, of Hilton & Hyland, has seen everything from a celebrity stalker who posed as Adnan Khashoggi to a buyer who claimed he was British royalty. (Incidentally, the royal family itself isn’t above being duped—in 2005, News of the World reporter Mazher Mahmood posed as a sheik interested in purchasing the estate of Princess Michael of Kent, tricking her into a damning interview.) Then there was a buyer who, claiming to be heir to a Chinese tobacco empire, “spent” $75 million on three of Umansky’s listings in a single afternoon—only to con another broker out of $5,000 before disappearing.

Lesley Martinson, broker-owner of Scottsdale Fine Properties in Arizona, had no qualms about showing a qualified buyer—one with a Wells Fargo bank statement indicating a balance of millions—a furnished $6 million home. The buyer seemed so legit that Martinson let her take prepossession of the house on a Friday afternoon, with the expectation that the funds would arrive on Monday.

They didn’t. “There was a series of glitches explaining why the funds didn’t come— and of course they all made sense,” says Martinson. As the weeks passed, Martinson grew suspicious. She called the buyer’s lawyer, looking up the phone number herself and ignoring the one on the letterhead. Sure enough, the documents had been forged. The “buyer,” who had pulled this scam before, was arrested.

However, most of these poseurs are harmless. “All they want is to see the houses,” Umansky says. Indeed, far more typical is Burt Minkoff’s story. Minkoff, a Corcoran agent in Palm Beach, Florida, once spent several days showing some 20 properties to a couple visiting from New York. They claimed they’d be buying a home by the end of their stay, so, at his customers’ urging, Minkoff canceled his New Year’s plans in Miami. But when he arrived to pick up his customers for a January 2 appointment, he discovered they had checked out of their hotel.

Like most agents, Martinson has learned from her mistakes. She now verifies prequalification documents she receives. “It’s frightening to think how real estate agents  didn’t do this before,” she says. “Definitely in this day and age, we have to do that due diligence.”

McGraw says she now trusts her instincts but acknowledges that skilled poseurs will always find ever more sophisticated ways to deceive. “It’s just part of the business,” she sighs. “Ninety-eight percent are real customers. The other 2 percent are just having a good time checking out the real estate.”