Rising mortgage rates and higher prices are likely to bring an increase in a concept known as equity sharing, especially for first-time buyers who are short on money for the down payment and closing costs.

Equity sharing works like this: In exchange for a slice of the value you build up over the years, a third party will spot you the cash you need to make the deal work.

The scheme has been around for years. Mission-based or publicly subsidized equity-share programs, such as community land trusts and limited equity co-ops, have helped thousands of families become homeowners.

Now, a dozen or more for-profit investors have entered the market or are about to, expanding the sector exponentially. But the various programs are not created equal. Rather, they’re all over the ballpark in their terms and conditions.

Consequently, “consumers need to be vigilant about protecting their interests,” says the Urban Institute’s Housing Finance Policy Center, an independent think tank examining the issue.

This is a “fast moving” concept, as at least 12 firms are “still in the launching stage and shopping for both customers and investors,” says Brett Theodos, a senior research associate at the policy center. That is, firms are seeking customers to borrow the money and investors to provide it.

The center is focusing its research around a number of questions, according to Theodos. And they are the same ones would-be clients should be asking to determine if equity sharing is right for them, and if so, which company’s program best fits their needs.

Here are the major variables to consider:

-- Charges: What is the all-in cost of participation, including up-front fees, servicing fees and third-party fees? Generally, they should be in line with what regular lenders are charging. Ask to see a complete list.

-- Terms: How long does the program last? Typically, they run for seven or 10 years, which is within the time frame in which most people sell and move on. But what if it ends before you are ready to sell?

You’ll probably be able to refinance, pay off your equity partner and have enough left over for a healthy down payment on your next place. But what if values have remained flat during your tenure as an owner? Or worse, what if values have gone down? Does your equity partner share in the downside as well as the upside? And if so, what portion of the loss does the firm cover?

-- Value: How will the value of your property be determined? By an appraiser, or an automated program? If it’s an appraiser, will he be hired by your partner or by you? And who determines the accuracy of the valuation? Also, who pays for it?

-- Termination: What happens if you want to end the pact early, before its term is up? Is there a penalty?

Say, for example, that you have a 10-year agreement with your equity partner, but you want to sell and move elsewhere sooner. Investors are expecting a certain return on their money, and by moving, you are cutting into their return on investment -- perhaps drastically. How exactly is this situation handled? And make sure the answer is in writing as part of your deal.

-- Restrictions: Can you obtain a home equity line of credit or a second mortgage based on the increased value of your property? If you are spending your equity for whatever reason -- perhaps a European vacation or remodeling project that will add value -- your partner will want to have a say. So, what are the rules?

-- Improvements: Are you allowed to make capital improvements such as an addition or finished basement? How are they taken into account in determining the investor’s share? If you pay for improvements entirely, do you get all of the extra value attributable to the improvements, or does your partner get to share in that, too?

-- Default: What happens if you don’t pay your property taxes, or can’t make your house payments and default on your loan? Again, ask to see the rules. A number of seniors who took out home equity conversion mortgages -- aka reverse mortgages -- lost their houses because they either didn’t realize they still had to pay their taxes and keep their homeowners’ insurance up to date, or just failed to do so.

-- Disputes: How will disagreements be settled? Will you be required to take your beef to arbitration or can you go to court? If it’s arbitration, who gets to choose the arbiter -- you or your partner?

Make sure you thoroughly discuss all of these issues before committing to any equity-sharing plan.

Even after 51 consecutive months of a below-normal supply of homes for sale, the picture for buyers this year is expected to be even more challenging, according to an analysis from Realtor.com, the website of the National Association of Realtors.

Active inventory in December on the site was down 11 percent compared to December 2015. As a result, 2017 has started with the lowest inventory of homes for sale since the recession, and possibly in decades, said Realtor.com Chief Economist Jonathan Smoke.

At the same time, online realty firm Redfin reported that inventory declined even more in December -- 12.7 percent -- to the lowest level in three years.

The lack of houses for sale was a challenge all last year, but a stronger “off-season” in the fall depleted the available homes for sale even more than is typical.

Now, with interest rates expected to rise to perhaps 4.5 percent or more this year, demand has become more intense. With fewer homes to look at, average views per listing were up 40 to 80 percent in the last three weeks of December compared to the same time in 2015, says economist Smoke.

“Multiple potential buyers seem to be interested in virtually every home on the market, even though we are in the slowest time of the year for sales,” he reports.

In its report, Redfin said of the homes sold in December, a third were under contract within two weeks of coming on the market.

“We’ve never before seen homes turn over so quickly at a national level,” said Nela Richardson, the company’s chief economist. “This tells us that buyers (were) not deterred by low inventory, election uncertainty and slightly higher mortgage rates. If anything, these headwinds are motivating them to act sooner rather than later.”

Borrowers who are having trouble with the outfit that collects their payments and pays their taxes and insurance, and who get no satisfaction on their first try to resolve the issue, need to kick it up a notch.

That’s the surest way to get the company’s attention, says Kevin Brungardt, chief executive officer of the RoundPoint Mortgage Servicing Corp., one of the country’s largest non-bank mortgage servicing companies.

“With social media these days, not to mention the risks of regulatory intervention, servicers have to be much more responsive,” says Brungardt, who suggests finding the name of the CEO or other top officer in the company and contacting that person directly, either by phone or email.

“There are so many different ways to connect and push back to get your issues addressed. And keep trying until you succeed.”

There’s still time to nail a house in the best month of the year for bargain prices.

According to an analysis of more than 50 million transactions over a 16-year period by ATTOM Data Solutions, people who purchased a house in February bought at an average 7.2 percent discount from the median price for all houses over the study period.

Eight of the top 10 days to buy are in February, with the other two being in January, according to ATTOM economist Daren Blomquist.

If you miss February, you can still obtain discounts -- albeit smaller ones -- in March and April, the analysis suggests. But if you wait until the period from May through September, you’re likely to pay a premium of up to 5 percent above the median.

Between 2000 and 2016, more sales took place in June than any other month. August was next, followed by July, May and September. The fewest sales were in February, January and November.

The spots with the largest concentration of second homes may not be where you think. It’s not the beach, but the mountains, according to an analysis of the nation’s 7.5 million seasonably occupied houses by the National Association of Home Builders.

In fact, 79 percent of the houses in Hamilton County, New York, were second homes in 2014, the latest year for which statistics are available. Some 74 percent of Forest County, Pennsylvania’s houses were second homes, as were nearly 73 percent in Rich County, Utah. None of the 10 counties with the largest concentrations contained an ocean beach.

Second homes accounted for more than 10 percent of the housing stock in 913 of the nation’s 3,300 counties. And in 357 counties -- 11 percent of the total -- 20 percent or more of the houses were seasonal.

Attaching a so-called “love letter” to your offer on a hotly contested property is often touted as a way to make your deal stand out from the competition. But you may want to think twice about doing so. And your seller may be wise to ignore your missive.

It’s not that letters to sellers don’t work. They do, especially when you are competing with several other potential buyers, according to dozens of realty agents who suggest them to their buyers.

With promises to take care of the house “just as well as you did,” make sure the gardens are tended just as carefully, or that your kids will love the place as much as theirs did, these letters tug at sellers’ heartstrings as well as their purse strings.

Some real estate associations and brokerages go so far as to offer templates and tips about just how to structure your letter. They even suggest pairing the missive with a cute little drawing of the property by one of the wannabe buyer’s kids, or maybe attaching an adorable photo of your wonderful family so the seller can get to know you a little bit better.

But there also are a couple of downsides to pouring your heart out in a “pick me, pick me” letter to the seller.

For buyers, these letters reveal that you really, really want the place -- so much so, that you are willing to list your reasons in longhand. So rather than be persuaded that you’re the buyer he wants, a seller could just as easily dig in his heels and hold out until you offer more than you wanted to pay.

Buyers might also get themselves into trouble if their intentions aren’t really to give the house the love they say they will. Say, for example, that the letter is simply a ploy to get the land, not the house, and you really intend to knock it down and replace it with a bigger, better property.

There’s probably nothing the seller can do about that other than hiss and moan a bit. But what if the seller chooses your offer over one that offered more money because he liked the looks of your family in the attached photo, and your letter was so meaningful?

In situations like that, sellers could be opening themselves up to a world of hurt in a fair housing complaint from one of the rejected “suitors.”

The Fair Housing Act prohibits discrimination based on an individual’s race, color, religion, sex, disability, family status or national origin. So consider this scenario offered by Denver real estate attorney Jon Goodman at the recent National Association of Realtors’ annual convention in Orlando:

A few weeks after you sell your house, one of the buyers who competed for it sees in the local newspaper that you sold the place for less than what he offered. Now suppose that that would-be buyer was a person of color, a “visible member of an oppressed minority,” and that they’d attached a photo to their “pick me” letter, from which you could easily tell the person’s race.

Or suppose the successful buyer belonged to your church, and the rejected one didn’t. Maybe the letter attached to the accepted offer mentioned in passing that the writer intended to attend the church down the street, and the seller just happened to go there, too.

In either case, a suit charging a violation of the Fair Housing Act lurks just around the corner, Goodman warned. “Fair Housing cases tend to go down when the market is bad, but they go up when the market is hot.”

The Colorado attorney, who describes himself as “a gladiator” for his clients, doesn’t advise buyers not to write love letters. Neither does he suggest that listing agents unilaterally keep letters from their clients.

Rather, his recommendation is to include in the listing agreement a clause that says, in effect, “pick me” letters will not be passed on to the seller. If the seller never sees the letter, he can’t get himself into trouble.

”Sellers should make their decisions for economic reasons, not because ‘this buyer is like me,’” he said. “It’s not supposed to be about black or white. It’s supposed to be about green.”

Goodman isn’t the only realty lawyer worried about love letters. So is Annie Fitzsimmons, a legal hotline attorney with the Washington Realtors organization.

In a podcast a couple of years ago, she told group members that they have no choice but to present all offers as well as “other communications” to their sellers. But the only documents sellers should consider are the written offers, and the letters from lenders saying the buyer has been approved for financing.

Fitzsimmons also advised her members to fully document the business reasons their seller chose the offer he did. Perhaps it contained the highest price, or maybe it allowed for the fastest closing date. Maybe it came with the largest amount of earnest money, or perhaps it contained no contingencies.

Whatever the reason, she said, by documenting it, there can be no ambiguities. And no one can come back later to charge you with discrimination.