The cofounder of a 'Shark Tank' success story shares the excellent advice Barbara Corcoran gave him during his first year in business

Cousins Maine Lobster

Barbara Corcoran taught Cousins Maine Lobsters to avoid opportunists.

When Jim Tselikis and Sabin Lomac appeared on the fourth season of "Shark Tank" in 2012, they had been in business for two months.

Their Cousins Maine Lobster food truck, which brought a taste of Maine to California, had a promising start, but was still largely unproven.

The cousins, however, had prepared so well and had such a solid business plan that Barbara Corcoran invested $55,000 for 15% of the company. Today it's one of the most successful "Shark Tank" companies. Cousins Maine Lobster now has 26 food trucks in 13 states, a restaurant in West Hollywood with up to 10 more on the way, and an online business. Tselikis said they are expecting revenues of just under $20 million in 2017, at a profit.

Because Corcoran took a decent chunk of the company when it was barely off the ground - the only prior funding was Tselikis and Lomac's personal $20,000 each - she became a business partner along for the whole ride.

Business Insider recently spoke with Corcoran and Tselikis on the last day of Corcoran's annual retreat with a selection of her favorite "Shark Tank" entrepreneurs, at Yankee Stadium in New York City. Tselikis told Business Insider that Corcoran is constantly giving them great advice, but that perhaps the best she's given came during their first year in business: "Everything that comes your way isn't a good opportunity."

The episode where they appeared aired in October 2012 and they received an onslaught of offers.

"When you come out of 'Shark Tank,' or you have some notoriety or exposure, there's a million things that come your way, from people that want to save you on shipping or insurance, or they want to build your trucks, or they want to do your logo and branding, or marketing, or website," Tselikis said. "But you start taking those things on and you forget the focus of your business."

Corcoran was there to temper their excitement and remind them why she invested them in the first place: She trusted their competency, not that of outsiders, and she thought they had a food truck concept.

Tselikis said he and Lomac internalized that advice, and it's still relevant.

"Establish yourself for what you do," Tselikis said he learned. "Do it well and do it really well until no one else can do it better."