Kevin O’Leary expects to finalize just three or four of the more than 12 deals he makes this season on “Shark Tank.”

“I only close one-third of the hands that I shake,” he tells The Post.

New York real estate mogul Barbara Corcoran has a better track record — about 70 percent — but admits she, too, has rescinded at least five offers during the show’s first four seasons.

“Everybody that comes on is well aware that it is a gentleman’s agreement and there will be a due diligence process for both parties,” executive producer Clay Newbill says.

Many deals fall apart during the months-long vetting process in which the sharks pour over balance sheets, test products and learn more about their potential business partners.

Corcoran, while reluctant to give names, shares a few of her deal-killers:

* “One service business said they had a patent, but they didn’t.”

* “I had one food business that didn’t close because everybody tasted their flavors and didn’t like any of them. It was also an all-natural product and the entrepreneurs didn’t want to put in any preservatives, so it had no shelf life.”

* “There was a product I was in love with, but when we got them at the office I couldn’t turn them on. They didn’t work.”

* “One children’s product had absolutely no margins. They were making no money. It sort of fell into the ‘I’m in love with my hobby’ category.”

The process of closing a deal begins moments after the wannabe business moguls step offstage — and months before the shows air Fridays on ABC.

Corcoran has an assistant hand each entrepreneur a “welcome packet,” she says. “It contains 20 questions about their business” and a signed copy of her latest book “with a ribbon on it.”

She then assigns a team of Columbia University MBA students to comb through every aspect of the company, idea or invention.

In cases where two or more sharks invest, each conducts his own research into the company.

On an episode that hasn’t aired yet, Corcoran and fellow shark Mark Cuban both agree to invest in the children’s product.

But after reviewing the same set of information, she chose to back out, while he moved forward.

“Venture investing is like a mating dance,” says shark O’Leary, who employs three full-time staffers and four interns to vet his show-related acquisitions.

“Both the investor and the entrepreneur have to want to enter into that marriage. There are all kinds of reasons it happens and doesn’t.”

It’s common practice, O’Leary says, for sharks to share resources during the due diligence process.

“If I invest in something that is not in my field, like a food product, I have no problem calling up Daymond (John) — who knows this space — and saying ‘Work on this with me, and I will give you a piece of the deal,’ ” he says.

Earlier this season, O’Leary borrowed the franchise due diligence team from Boston Pizza to help research a “Shark Tank” investment in Texas.

That deal, he says, still hasn’t closed — but may in the future.

Each shark has his own way of walking away from a deal that doesn’t work out.

“I send a very clear ‘Dear John’ letter,” Corcoran says. “It doesn’t usually come as a shock. Everyone receives it well.

“I find if on a Skype call I say, ‘This isn’t going to work out, and let me tell you why’ they hear you but they don’t remember it. And you spend a lot of time saying it over and over again.

“When you write it all out they have it in hand and they can digest it. You are also giving them a template by which they can change their business.”