How Scammers Rent Out Occupied Houses

— -- When the owners of an Indiana home recently listed it for sale, they got an unexpected surprise: a rental scam targeting their address.

"People were getting out of their cars. They were coming up to our front door, ringing our doorbell, looking into our windows," homeowner Amy Hagans told ABC News after an ABC News reporter noticed a story about her plight that originally appeared in The Star Press.

The people were responding to a Craigslist post advertising a three-bedroom, two-bath house, with a big backyard that was available to rent for just $750 a month.

"I fell in love with the house. The yard was humongous," said Patty Costa, who came to see the house in Muncie, Indiana.

Costa said the home was "perfect" for her grandchildren. After exchanging texts with the person who posted the ad, she wired the person a $275 deposit and then came to see the house herself.

When Costa approached the home, she learned that the deal was too good to be true. The Hagans' had posted a sign saying, "Our house is not for rent" to alert people to the scam.

"I opened the door to see a lady standing on my porch, reading the sign on our front door," Hagans said. "I felt terrible about the whole situation."

It's a scam being played out in housing markets across the country.

"It's very, very simple to do these types of Internet scams. It's very easy to hijack an existing listing," said Austin Berglas, the head of U.S. Cyber Investigations for K2 Intelligence, an investigative consulting firm.

The process is called "scraping."

Scammers create fraudulent rental listings using photos and details from legitimate postings already online.

In the Hagans' case, the scammer may have used images from the real estate company's website where the Hagans' had posted their home for sale.

According to the FBI, scams like these cost Americans nearly $20 million in 2014. And the bureau estimates the actual number of cases could be 10 times higher because many aren't reported.

These types of scenarios also exist in the vacation rental market.

When Cherry McCaffrey used a rental website to book a vacation house in South Lake Tahoe for her extended family, they found the door unlocked when they arrived.

After they settled in, the owner showed up, not knowing his house had been rented out.

Experts say there are ways renters can protect themselves. First, never wire money. Second, try a "reverse image search" for the listing photos on a site like Google.

If images from that listing appear on multiple websites, renter beware. And third, use common sense.

"I think the best tip, is really, if it looks too good to be true, it most likely is," Berglas said.