Longtime friends Khat Rabbani and Ashley Williams began selling hair extensions out of their cars in 2011, with no idea how far their initial $2,000 investment would take them. By the end of the year, it had turned into $70,000, and then $700,000 the year after that.

They opened Hair Are Us, their flagship store in Atlanta, which was joined a year later by a location in Miami. Revenue exceeded the $1 million mark, but not without sacrifice.

"In the beginning we put everything on the line," Williams said. "We didn't do anything else but sleep and eat Hair Are Us." Luckily, they knew who their future customers were, and they knew how to target them.

"We went to colleges, we went to all your different nightclubs, restaurants, the malls, anywhere you can think of," she said. "We were there, leaving fliers. And we realized that it was working when the phone started to ring." The phones haven't stopped ringing ever since.

Today, Rabbani and Williams are opening a Los Angeles location, launching a product line and writing a book about the hair business. But the downside of all that rapid growth is that they're clearly overwhelmed and having trouble prioritizing.

Marcus Lemonis of CNBC's "The Profit" suggested that they focus on their online store. It's their biggest revenue source and has the most growth potential.

Hair Are US founders Ashley Williams, left, and Khat Rabbani

Source: Hair Are Us

"Your time management should be spent 50 percent of your time on figuring out how to grow the online business, 25 percent of your time being marketing geniuses, which you guys already are, and then the rest for the locations," he said. "And if one and two aren't right, don't do three."

Rabbani and Williams also mentioned that they had been toying with the idea of franchising. While Lemonis agreed that it can be helpful in building a business, he urged the entrepreneurs to hold off for now.

"Franchising's an important thing," he said. "But if you have the capital to do it yourself, you may want to make all the money for your business before you let everybody else make money on your business."

He told them that when the time to franchise rolls around, they should carefully consider whom they sell their business to. He recommended putting future locations in hair salons, where the staff's hair care knowledge is equal to theirs.

"I would much rather be selling my franchise through somebody who knows the business, as opposed to somebody who says, 'Oh, I want to make $20,000, I'll buy one,'" he said.

Rabbani and Williams took Lemonis' advice. They have put aside the idea of franchising and focused instead on expanding online, and to sweeten the pot, they gained the endorsement of tennis star Serena Williams.

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