Police say it happens more than you might think.
Nick Kaiser lived in an Antioch home for 12 years, but he lost his job and fell on hard times. He moved out so his realtor could sell it.
"He told me he had a prospective buyer and that it should be a short time before the home is sold," Kaiser explained. "So next thing I know. I get a call and he says that this lady says she's living there."
Kaiser's neighbor, Augustine Gallegos, watched the whole thing unfold.
"These people moved in there," she recalled. "One of them says, 'My name is Theresa, we're renting this house.'"
She was so convincing that his wife even gave the new family roses to welcome them to the neighborhood.
"All the time we thought they had rented the house but actually, they had broken the lock and gotten into the house," Gallegos said.
Kaiser's realtor called police who came and searched the home.
"They said they found a couple of shotguns and some other firearms and a SWAT vest. And, they removed all the stuff that day," Kaiser said.
Michael Tembey has seen it all during his years as a realtor in Brentwood. He has seen squatters leave homes trashed with graffiti on the walls, carpets stained or ripped out, and appliances broken or stolen. He says more than two percent of his 190-plus listings the last two years have been taken over by squatters.
"Normally, we did not see this," he said. "I think in this economically challenged times, individuals, human beings are challenged with loss of jobs."
Police in Antioch do not break out squatting complaints, but say most agree that once squatters break into the property it can be difficult to get them out.
Gus Kramer is the tax assessor for Contra Costa County and a landlord himself.
He told ABC7, "Once the squatter has taken over, you go through the same process you evict the tenant who's not paying their rent. And, it takes about 30 days."
But, Tembey says he has seen some evictions take as long as six months, and he thinks the number of squatters will continue to grow.
"So, as time has gone on, the issues have increased and I think we will see it continue to increase," he said.
As for Kaiser, he had to pay $400 to clean out all the junk left by the squatters. The sale of his home fell through and the bank foreclosed on the property. He had one thing to say to the squatters.
"What gives you the right to come to my property and stay without paying when I struggled for years and years just to make my house payment, and then have it pulled out from under me? Why do you get to live there free?" he asked.
Kaiser filed a complaint against the squatters but no arrests have been made in this case.