The letter arrived in Robin Roberts' mailbox innocently enough late last year. The envelope bore her name and her Mount Airy address. Neatly folded inside was a piece of paper, what appeared to be a handwritten note.

Basically, the letter said, someone had noticed her house. And in no uncertain terms, it asked: Would she consider selling it to them?

"I'm not late on my mortgage, I'm up to date on my taxes, there's no way we're in financial distress," said Roberts, 45. "Why would we entertain an unsolicited sales letter?"

"I feel like this is just a scam," she added.

Forum after forum online is dedicated to letters such as these, with homeowners worried about what these solicitations in their mailboxes really mean.

It's a legitimate concern, with possibly thousands of homeowners receiving letters such as these each year. The messages often come unexpectedly — and with few details offered. Like Roberts, the recipients are often left with more questions than answers: Is the letter a scam? Does it mean something is wrong with their property? Or could it be a signal that investors are speculating their neighborhood might be improving?

"Obviously, with the way the internet is today, and the way the real estate market is changing, buyers themselves can do a lot of searching for homes themselves," said Dylan Ostrow, a Realtor with the Rosenthal Group of Berkshire Hathaway Home Services Fox & Roach Realtors in Center City.

Letters like these "can be legitimate," Ostrow said, "but you have to exercise caution."

When Roberts received her letter -- the latest of many in recent years — her gut reaction told her to throw it away. So in the trash it went.

But not all homeowners are like her.

For nearly 10 years, Joshua Pireda and Marat Tsirelson, both executives with the residential development group GM Home Inc., have been sending letters to homeowners such as Roberts throughout the Philadelphia area. In a simple four paragraphs, they explain that they would like to buy someone's home "as-is," their letter states, "meaning you don't have to make any repairs."

Pireda and Tsirelson say they understand Roberts' and other homeowners' concerns. But they say they are legitimate.

Licensed themselves and using licensed subcontractors, and with a staff of about 15, Pireda and Tsirelson say they are in the business of "rehabbing" homes — basically fixing and flipping them. They distribute nearly 2,000 letters to homeowners each month. Part of it is a marketing tactic, they say; the other part, a true solicitation to buy a house quickly.

"Our goal is to purchase homes that are rundown," said Tsirelson, 30, GM Home's president. "We rehab them top to bottom and sell them to the millennial market."

Targeting properties in Philadelphia, Montgomery and Bucks Counties, Pireda and Tsirelson said, the letters are not the only ways they have found homes to repair. But it's a strategy that has worked, they said: One to two sellers each month sell their homes directly to them because of the letters, a process that "allows them to pay a seller more" because no Realtor commissions are involved. For a two-story rowhouse in South Philadelphia, they said, they pay, on average, $80,000 to $100,000.

"I guess from a first glance it might be scary or shocking," said Pireda, 30. "But when someone calls, I have a conversation with them. If they don't want to sell their house, that's fine."

Mostly, Pireda said, sellers should be cautious — and do their homework. It's a sentiment Ostrow seconded.

"When it comes to big purchases, big money, I'm always cautious of what I receive in the mail," Ostrow said.

Even if the solicitations are legitimate, he had one piece of advice: "Hire a Realtor to get a true touch on the market."