When Jack Black's Polka King comes selling investments, you should run

• Amid the comedy, new Netflix offering has some valuable financial lessons in "Polka King."
• Beware the bait-and-switch sales tactic.

Source: Netflix

Jack Black in "The Polka King."

Netflix is out with the next installment of its unintended financial education series.

Last year it was "Ozark," where Jason Bateman played a crooked financial advisor who shreds the fiduciary rule that says you must protect your clients' interests faster than the New England Patriots' secondary.

Available now on the video streaming service is "The Polka King," a fictionalized comedy about the nonfiction story of a Polish immigrant, Jan Lewan, who gained some fame as the "Polka King" of Pennsylvania coal country in the '90s. Played by comedian-actor Jack Black, Lewan just wants to be loved and live the American dream.

Unfortunately, living the dream takes money, a lot more than Lewan can muster playing weddings and other small-time gigs with his polka band, as well as manning a gift shop with his wife (played by Jenny Slate) in Hazleton, Pennsylvania.

So, Lewan stumbles on another idea.

When an elderly couple, enthralled by Lewan's upbeat and kitschy polka shows, wander into his shop, he entices them to invest in "Jan Lewan" enterprises. He tosses a thin pamphlet across his desk and tells his would-be investors to think it over.

They, of course, fall for his charms and while grumbling how they've been mistreated by stockbrokers and Wall Street, fork over their money. You can see how this will end.

To make sure you don't fall prey to the same type of con, consider these lessons:

Don't mistake affability for financial savvy

One of the reasons con artists like Lewan are able to raise money from unsuspecting marks is that they are just so darn nice. Lewan/Black always inquires about family, and his over-the-top enthusiasm for his dubious investment schemes are infectious.

Never confuse this with doing your own due diligence. Check out the offering carefully. Is there a business plan? Are audited numbers of income, expenses and potential future profits available? No? Then pass. Who are the managers of the business? Find out and Google them. They won't tell you? Then pass.

Charm is never a substitute for actually knowing what you are doing.

Older investors are often prey

Sad, but true. Seniors often fall for this type of con more than other age cohorts. Reporting by CNBC's Kelli Grant on elder fraud and abuse showed that this is a $36.5 billion a year issue.

Bait and switch

In the story, one older couple corner Lewan in his office and demand their money back (which of course has swelled from phony returns). As he's writing out a check that he knows would be sure to bounce, he lets slip that he's starting a new fund, one with "guaranteed" returns of 20 percent and only open to a select few. The couple, with dollar signs flashing in their eyes, tear up the check and immediately invest even more money.

Never fall for these high-pressure, better-get-in-now-before-it's-too-late tactics.

Unregulated securities are, well, unregulated

In the story, Lewan starts selling what's described as promissory notes, likely unsecured ones at that, meaning that they're not backed by any physical assets. Of course, he skips an essential step, registering them with regulators.

Selling unregistered securities is a particularly ripe area for the not-so-above-board; FINRA, the brokerage industry's self-funded regulator, has called them out in investor alerts.

Generally, selling unregistered securities is restricted to so-called accredited investors, those who by virtue of high annual income or assets are deemed to be sufficiently knowledgable to evaluate the risk or sustain a loss. That doesn't always happen.

While the authorities eventually step in and shut Lewan down, it's not before the damage is done. That should be a warning to you. Don't rely on regulators to catch these things before it's too late.

There is no free lunch

Anytime someone promises you "guaranteed" returns from investments, they're engaging in some magical thinking. In fact, the smartest character in the movie is Slate's skeptical mother, who is convinced, correctly, that Lewan is up to no good.

Later in the film, when one bilked older couple confront her in a shopping mall parking lot over her son-in-law's dishonesty, she berates them: "You idiots, why did you think you could get 12 percent, when the bank is only paying 3 percent!" (She then eggs their car, just to make the point).

Anytime you're promised outsized returns, it's more likely fantasy than fact.

By the way, Lewan eventually conned investors out of almost $5 million, according to the show. And spent five years in prison.

He has vowed to pay those back he scammed — from polka shows.