Just in time for March Madness wagering, which is now legal in New Jersey and six other jurisdictions (besides Nevada), Showtime’s new documentary “Action” takes viewers into the splashy world of sports betting. Presenting what director Luke Korem describes as a 360-degree view of a multibillion-dollar industry, the four-part series debuting at 8 p.m. Sunday shows people winning, losing and often happy to break even in a pursuit that is rarely profitable for anyone but the house.

“Sports gambling is fun,” Korem tells The Post. “It’s exciting and an adrenaline rush.” As to what drew him to make the docuseries, he says, “The legalization of sports betting will change the way we view and consume sports. It will continue to grow, and we need to have a conversation about the industry.”

Over “Action’s” four hours, viewers see everything from a high roller strategizing on bets in the ornate Elvis Presley suite at Westgate Las Vegas (where Presley once performed) to an ardent gambler doing similar noodling in the much more modest confines of his disorganized kitchen.

Central characters include the professional sports bettor William “Krackman” Krackomberger, whose partner uses a computer model to find advantageous wagers; Jimmy Vaccaro, a veteran handicapper who was director of sports marketing at Vegas’ South Point Casino (he has since relocated to Rush Street Gaming in Pennsylvania); and a flashy showman who calls himself Vegas Dave.

The most polarizing character in the doc, David “Vegas Dave” Oancea ostentatiously drives luxury cars and boasts of his “villa” with 17 TV sets. Characterized by gambling-world insiders as a tout, he calls himself a sports information consultant. Whatever the handle, Oancea — who recently pleaded guilty to “causing a violation of record keeping,” stemming from allegations he used other people’s Social Security numbers to open player accounts at various casinos — promotes himself as a gambling expert and sells picks to recreational bettors who hope to gain an edge. He appears to be making millions a year from them, if not from wagering itself.

“My best plays are ‘whale plays,’ ” Oancea says, before dropping what sounds like an over-the-top statistic. “I have won the last 21 of 22 whale plays.”

Clients pay hundreds and even thousands of dollars for his picks. Many in the gambling industry believe that touts sell tips to their customers — Krackomberger cuts to the chase, calling them “scamdicappers” instead of handicappers — that raise false expectations and make impossible promises, and these touts are more expert at marketing than they are at selecting winners.

In the documentary, Oancea claims to have a 75 percent success rate, in a world where winning 57 percent of the time provides enough of an edge to make any sports bettor wealthy (though, for somebody in Oancea’s trade, the prospect of losing 43 percent of the time hardly seems like the sort of thing that unsophisticated gamblers would spend good money on). Krackomberger and Vaccaro both express serious doubts about Oancea’s 75 percent brag.

During an interview with The Post, even Korem agrees.

Told that his win rate sounds improbable, Oancea gives the verbal equivalent of a dismissive shrug. Then, he claims to have won $5 million during a six-month period in 2015 (it is unclear whether that sum is net or gross).

“I don’t care what people say,” he says. “I don’t expect everybody to understand.”

Certainly, Krackomberger does not. “The viewing audience shouldn’t be swayed [by his claim],” he says. “I would never talk to him.”

Generally skeptical of touts — who, detractors argue, would be betting millions rather than selling picks if they could win 75 percent of the time — Korem says that Vegas Dave is in the documentary for good reason and that nobody “gets treated with kid gloves.”

“Vegas Dave is part of the sports betting ecosystem. We think he is a prime example of a certain type of person,” Korem says. “I pride myself on letting the audience have an opinion on each person and draw their own conclusions.”

As to what those conclusions might be, Korem is giving away nothing. “We follow several of Vegas Dave’s bets and picks and you can see how they work out.”