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?

Donald's Trump "university" isn't the only school of higher learning in hot water these days. It's joined by the "fix and flip" seminars sold by Armando Montelongo, the onetime star of the A&E series "Flip This House."

In a federal civil suit filed in San Francisco this spring, some 160 students claim they paid thousands to attend Montelongo's classes that would supposedly teach them how to buy run-down houses, fix them up and sell them for a quick profit. But, the suit alleges, the courses served only to enrich Montelongo.

According to Montelongo's hometown newspaper, the San Antonio Express-News, "students typically paid $1,500 for an introductory course, where they were recruited for 'bus tour packages' that cost up to $54,000. ... Classes on 'asset protection' cost $27,000 more. 'Market domination,' cash flow programs and master mentor classes cost up to an additional $55,000."

The suit maintains that Montelongo and his companies have "destroyed livelihoods, wrecked marriages, driven students into clinical depression and even resulted in suicide."

In an email to the Express-News, Montelongo's attorneys essentially dismissed the suit, saying it was filed by a bunch of lazy students who couldn't follow the pitchman's instructions.

Of the "more than 1.5 million people" -- hold that thought -- who have taken the classes, the email said, the "small group" of plaintiffs "have decided continuous hard work is not for them. Now, they have chosen to try and make money the easy way by clogging up our legal system with a frivolous lawsuit."

The suit accuses Montelongo and his companies of violating the Racketeering Influenced and Corrupt Organizations (RICO) Act by committing wire fraud and conspiring to deceive investors over a number of years. It estimates actual damages at $4 million, but triple damages can be sought under the RICO law.

Back to that "1.5 million people" figure: yikes. That's a lot of customers. No wonder Forbes once estimated Montelongo's net worth at $200 million.

Had the disgruntled students -- and possibly many others who have not come forward, perhaps too embarrassed to admit they might have been fleeced -- done a little sleuthing, they might have saved themselves a lot of time and money. An online guide called "The Top 20 Real Estate Gurus: The Good, Bad and Ugly" gives him just one out of five stars, and the Amazon reviews of his paperback, "Flip and Grow Rich," are less than scintillating. "The 'secret' revealed in this book is that you need to sign up for Armando's seminar," said one reviewer. "Don't waste your money."

An 2013 article in Forbes describes him as a "house-flipping huckster" who offers "long weekends of questionable advice, raucous showmanship and tours of foreclosed homes in some of America's poorest sections." Writer Abram Brown asked him to produce alums of his seminars who made millions by using his methods, but he either wouldn't or couldn't.

Whether the suit against Montelongo will prove successful is hard to say. But he's probably right about one thing: Millions of people have attended his and other so-called gurus' seminars.

As an owner of rental houses, I see the handiwork of these "instructors" almost weekly.

In just the last few days, I have received four letters and postcards asking me if I want to sell a property. Some are typed, some are made to look handwritten (while still being mass-printed), but they all say essentially the same thing. They promise a quick, clean, "as-is" cash sale -- no sales commission or extra fees. They'll even pay all closing costs. What they don't say is that they only want to give me half what the place is worth on the open market.

What this tactic says to me is that either a lot of people have taken the same class, or a lot of these get-rich-quick guys are teaching the same thing.

The advice here is to stay clear of anyone who promises you'll earn a fortune by following their investing techniques. If it's so easy, why are they peddling seminars, books and videos instead of flipping houses full-time themselves?

It may look simple on "unreality" TV, but it isn't.

(Next week: How to spot a scam artist.)