Remember the "k-i-s-s-i-n-g" song from when you were a kid? "First comes love, then comes marriage, then comes a baby in a baby carriage."

In the old days, a mortgage usually came after the baby carriage. But fast-forward to modern times, and many couples are buying a house together before getting hitched. Changing the natural order of things could be a big mistake, warns Matt Parker, a Washington real estate agent who hangs his shingle with Keller Williams Puget Sound.

"While the numbers and studies are complex, the reality of a successful, mature partnership is not," says Parker, author of "Real Estate Smart: The New Home Buying Guide." "Make a firm decision on your relationship before you make a firm decision on your home."

Even co-habitating without a legal agreement is not a good idea, Parker writes. The numbers say that living with someone before marriage equates to lower marital satisfaction, more marital conflict, higher rates of infidelity and a higher likelihood of divorce.

"The relationship should come before your housing choice," Parker told me in an interview. "Getting out is far more difficult then getting in."

So fast-forward again, past the courting stage to the point where you're talking marriage. Admittedly, that comes much later these days than it used to -- so much later, in fact, that the prospective bride and groom may have created their own significant assets by that point. Perhaps a prenuptial agreement is in order.

Will that prenup impact your ability to obtain a mortgage?

Usually, the answer is no, says Karen Linehan-Wilson with 1st Advantage Mortgage in Lombard, Illinois. Generally, lenders do not ask about prenups. Barbara Sparks, with Envoy Mortgage in Houston, mostly concurs. Prenups "are acceptable," she told me, "as long as the agreement is court-ordered and complies with state laws."

Divorce is another thing entirely. The statistics aren't great. If there are children involved, buying a house after the split -- even long after the split -- becomes much more complicated.

When a would-be borrower has a divorce in his or her history, lenders want to see the marital settlement agreement, says Matt Weaver of Finance of America Mortgage in Boca Raton, Florida. Specifically, they are looking to see if the applicant pays or receives alimony or child support. As far as the underwriters are concerned, according to Weaver, there is no difference between alimony and support, even though support is usually tied to the age of the child/children.

If you have been receiving either type of payment continuously for three years and will continue to receive it for at least six months, says Weaver, you can count it as income. Of course, it must be verifiable, says Sparks. For child support, she says she confirms the children's ages to be certain the payments will continue for at least 36 more months.

If you pay alimony or child support, on the other hand, it counts against you in your debt-to-income calculation -- "in totality," says Weaver, no matter how much longer you have to pay.

Well, almost. If you have six months or less to go on your support payments, it's possible to make an exception. But otherwise, no.

"It's counted just like a car payment," says Weaver. "It's a liability that's no different than any other type of installment loan."

A copy of the divorce decree or court-ordered support payment is necessary to verify what you are paying or receiving. And if the terms of those documents have been modified, Sparks cautions, "a fully executed court order" is required to confirm the changes.

If your former spouse is paying inconsistently, you're going to run into trouble. If the lender cannot verify that you are receiving alimony or support payments regularly, month in and month out, you won't be given credit for it as income.

Another common problem with these kinds of payments is shared expenses: for example, jointly paying for the kids' braces. If your ex pays the orthodontist instead of you, it upsets the monthly verifiable trail of support payments. Here, Weaver says the important thing is to keep the trail intact: You get the money, and you pay the orthodontist.

One more possible challenge: If you want to buy another property while you are still in the throes of divorce, you should execute a "quit claims deed" to your current house and your soon-to-be former spouse should sign a release of liability.

If the split is less than amiable, good luck getting your ex to sign anything. Weaver calls that "a common cause of frustration" for the once-married borrowers he sees.

That's why he, like Parker, says not to rush into homeownership with your current love. Give it some time.

The first thing you should do after you move into a new place is change the locks.

OK, maybe you could pop a bottle of champagne first and toast your new home. And possibly unpack the kitchen. But after that, change the locks.

Not just the front door lock, either, but also the side door, back door and garage door. If you have electric garage door openers, change the combination on the remotes.

It's not that the folks who owned the house before you were thieves or killers, although you never know. But there's no telling how many keys are out there, given to friends, family and neighbors of the previous residents. You have no idea who these people are, and they have access to what's now your place.

Changing the locks is so important that some agents have taken to giving their clients new lock sets -- or even hiring a locksmith -- as a housewarming gift.

When she orders a home warranty for her buyers, Wanda Kubat-Nerdin of PK Real Estate in St. George, Utah, also includes a complimentary re-keying. And she advises them to "get it done right away."

A visit from a locksmith is also Gwen Fowler's way of saying "thanks for your business." The South Carolina broker says her go-to locksmith "gives me a good price, and goes before the buyers move in. ... (It provides) peace of mind for me and everyone else in the process."

Just when mortgage cops think they've seen it all, a new kind of fraud pops up. The latest scam: reverse occupancy.

Whereas some people say they intend to occupy what's really an investment property in order to obtain a lower finance rate, in a reverse occupancy scheme, the buyer says he intends to rent the house and uses the potential income stream to help qualify for the mortgage.

The maneuver is being used by would-be owner-occupants who don't otherwise have enough income to pass muster, according to Kevin Ludden, fraud industry relations manager at mortgage giant Fannie Mae.

The reverse occupancy liar gets a somewhat higher rate because he supposedly is buying an investment property. Plus, he has to put more money down than an owner-occupant would. So why should anybody care?

Because if there is no income from rent, there is a far greater chance that he won't have enough money coming in to make the monthly payment.

Besides labeling the house an investment property and making a large down payment, two other red flags include the purchaser being a first-time buyer with minimal or no established credit, and having a low income but significant liquid assets as authenticated by bank statements.

In 2014, for the first time in more than 130 years, young adults ages 18 to 34 were more likely to be living with their parents than to be cohabitating with a spouse or partner in their own homes or apartments, according to the Pew Research Center.

The main reason: Fewer people are choosing to settle down romantically before age 35, the tipping point into middle age.

Dating back to 1880, the most common living arrangement among young adults has been living with a romantic partner. But sometime around 1960, that type of household peaked, Pew says. Back then, 62 percent of all 18- to 34-year-olds were living with someone else under one roof, while just one in five were still residing at home.

But in 2014, nearly 32 percent of people in this age group were living at home -- whether "still" or "again" -- vs. 31 percent who lived with another person in a separate household. That's not a record, though. Around 1940, 35 percent lived with Mom and/or Dad.

"What has changed, instead, is the relative share adopting different ways of living in early adulthood, with the decline of romantic coupling pushing living at home to the top of a much less uniform list of living arrangements," Pew Research reported.

If you think lot sizes seem to be shrinking, you're very astute: The median lot size of a new single-family detached house sold last year dropped under 8,600 square feet -- about a fifth of an acre -- for the first time since the Census Bureau started keeping track.

Having trouble visualizing 8,600 square feet? Paul Emrath, an economist with the National Association of Home Builders, says 5.6 median-size lots would fit onto a football field.

John T. Reed is a real estate investor and prolific author. He's also a pain in the backside for the modern-day snake-oil hucksters who peddle get-rich-quick real estate schemes on late-night TV and radio.

Their spiel goes something like this: Attend their seminars, take their classes and buy their books and DVDs, and you'll make millions buying houses on the cheap and reselling them in short order.

Reed says he's often asked what he thinks of a particular instructor or his programs. He isn't familiar with the work of every one of these charlatans, but he has built a list of observations that potential customers can use to separate the bad guys from the good guys. Here's a short synopsis of some of the points on his "B.S. checklist."

-- Emphasis of luxury lifestyle. The best teachers rarely mention how well they've done and don't need to wear their supposed affluence on their sleeves. Those who throw the bull have their photos taken with Hawaiian backdrops, stretch limos and Lear jets to help create an aura of financial success.

-- Best of the best. The bad guys' bios are full of baseless, subjective phrases like "the leading" this or "the No. 1" that. Watch out for words like "innovative," "famous" or "spectacularly wealthy."

-- No regrets. Every real estate investor has made at least one bad deal in their lifetime, but not the hucksters. They rarely point out the pitfalls of the business. Everything has a downside, but not to these guys.

-- No bad news. Similarly, according to the snake-oil salesmen, no new court decision, law or economic trend ever holds bad news for the real estate sector. These rotten apples always see opportunity, even during times when smart investors should retreat to the sidelines.

-- Universal techniques. Another way that suspect counselors boost sales is by trotting out "new," and often obscure, methods. But rather than explaining when one tool or another is appropriate, they leave the impression that all techniques are suitable for every deal. In reality, there is no one-size-fits-all real estate strategy.

-- Motivation. These false prophets wrap too much of their appeal in motivation. There's nothing wrong with trying to rally the troops, but too many "you, too, can do it!" platitudes border on the dishonest.

-- False claims. Virtually all the fake gurus claim to practice what they preach. Baloney. They spend far more time on their seminar business than on their investments, if they have any at all. They may have done some deals -- maybe even many deals -- but that's ancient history. Now they are selling, selling, selling.

-- False offers. The bad guys sometimes offer to join their students in investment deals, but they never do. They may invest in one or two deals someone else brings to the table to be able to say they do, but for the most part, money never comes out of their pockets -- it only goes in.

-- Without money. To overcome the objection of students who really have no money to invest, the dishonest professors stress no-money-down techniques, which are fundamentally unsound. These schemes are "a way to part fools from their money, not a way to invest in real estate," Reed says.

-- Red flags. Treat these words as flashing "steer clear" signs: surefire, cinch, always, easy money, risk-free, safe, magic, bulletproof and automatic. No such thing, at least not in real estate.

-- Fake testimonials. When real people testify to their success using the guru's techniques, they use their full names and locations. When paid actors do so, they only use their initials or their first name, so you can't check them out and confirm their validations.

-- No recording. The instructors who bar you from recording a free promotional seminar do so to prevent you from having evidence of the fraud they are perpetrating.

-- Hard sell. If there's a push to buy increasingly expensive classes, books and DVDs, you are in the hands of someone who thinks they have a sucker on the line.

-- Show me the love. They'll tell you they're not in it for the money. Rather, they are telling the world how to make money in real estate out of the goodness of their hearts. Yeah, right. If so, why not just give away their knowledge, instead of charging thousands for it?