Seventy-year-old Mary Ann Welch had always wanted to pass down the two-bedroom Sunnyvale home she inherited from her mother to her seven grandchildren.

So she was astonished when she found a letter in her mailbox in 2016.

“It said we’d like to buy your house, and I was surprised because I had not put it up for rent or for sale or anything,” she said.

The letter offered to pay Welch $750,000 for a house that is a young techie’s dream. It’s a house that is within walking distance of Apple, Google and LinkedIn offices. And it’s a house that currently is worth more than $1.5 million. The letter even came ready with paperwork, complete with directions on where the sender hoped Welch would sign her consent to sell.

“I saw the contract for me to sign and I was furious,” Welch said. “If I had Alzheimer’s or if I was demented at all, I would have signed it thinking I would get all this money. I wrote a letter to the (district attorney.) If they’re doing it to me they’re going to be doing it to others.”

“They” are.

“We’ve been seeing an uptick in cases that involve direct solicitations to elderly homeowners potentially well below market value,” said Cherie Bourlard, Santa Clara County deputy district attorney.

No official statewide stats exist on real estate fraud against seniors, but Bourlard said it’s enough of a problem to merit warning the elderly. She believes California’s super-heated housing market is driving scammers, and so is the age of their targets.

“They have no idea of the value of the homes they’re sitting on,” Bourlard said. “They remember buying their home for $40,000 but in these crazy upswings of market value, they have no idea their property might be worth $800,000, $1 million, $2 million.”

Bourlard said some elderly victims of real estate fraud have just enough mental capacity to get them into trouble.

“They might not clearly understand what they’re doing,” Bourlard said. “But they have enough capacity to where the transaction is not voidable. Studies show as we age, we become less savvy in financial transactions.”

Real estate opportunists find their elderly prey by trolling public property records. Then, they make contact.

“Direct purchasers are looking at assessor’s records and determining homeowners, who have very low assessed values, are likely to be elderly homeowners and are targeting them with fliers,” said Duane Shewaga, Santa Clara County real estate fraud coordinator.

Some of the fliers ask ominous questions like, “Do you want to cash out before war with North Korea breaks out,” or “Third notice, how much longer before I hear from you?”

“The homeowner says I never got a first or second one from you,” Shewaga said.

It took two notices to 84-year-old Carol Law and her 89-year-old husband George Law offering to buy their one-acre lot in eastern San Diego County before they got mad. They estimate the land is worth $50,000. They were offered $800 in cash.

“The first time I thought it was a stupid joke,” Carol said. “The second time I thought this guy is up to something.”

They speculated the person carefully picked them to make a low-ball offer.

“It looks like he was thinking, `OK, these guys have had this since 1979 they’re very old now,’ ” Carol said. “They probably are a little goofy.”

San Diego County prosecutor Valerie Tanney said some scammers go door to door to find senior homeowners, or they go to public places.

“I’ve had numerous cases where they approach and befriend people and use religion and the trusting nature of people at churches to victimize,” Tanney said.

Strangers aren’t the only ones conning the elderly out of their real estate assets. Loved ones try too.

“We get complaints from one family member against another family member that the person caused a relative to alter what was their previous estate plan at a time when that person didn’t have the capacity to make that decision,” Tanney said.

She advised seniors and sincere relatives to educate themselves on current scams. She urged people to contact authorities to report real estate fraud quickly to police and district attorneys’ offices. She also advised seniors not to sign any paperwork without first consulting an expert such as a lawyer, a financial planner or a real estate agent.

California Attorney General Xavier Becerra suggested that seniors save every document in case a real estate deal goes south.

“Always, keep good, good evidence,” he said. “Keep your records and know there are people you can turn to.”

The California Dream series is a statewide media collaboration of CALmatters, KPBS, KPCC, KQED and Capital Public Radio with support from the Corporation for Public Broadcasting, the James Irvine Foundation and the College Futures Foundation.