The House of Dereon, named after Beyoncé's seamstress grandmother, is just two years old. In these early days, Beyoncé's fame is a key factor.
"She's the marketing plan for us," Tina Knowles said. "Because we don't have these big huge budgets, we've had to be creative. Like, for instance, our launch was on the Oprah Winfrey show — you can't get better than that."
But better still for business is the interplay between Beyoncé's fashion and music careers.
The hoodie that Beyoncé wore in the video for her No. 1 one song "Irreplaceable" happened to be available in stores — and Knowles said they sold out. The company reprinted the sweatshirt and sold out again.
The payoff between celebrity and business is clear, but Knowles also thinks about the down side.
"I always worry that if anything is not great, that it will reflect on Beyoncé personally – because people are not going to say, 'Oh well, that's House of Dereon,'" she said.
But Kathy Lee Gifford's fate supplies a cautionary tale in the celebrity apparel business. Her Wal-Mart clothing line was a success — until it faced charges of unfair labor conditions.
"Her brand basically created a major downfall and affected her celebrity status in total, because of the fact that she was, her brand was implementing sweatshop rules," Cohen said.
But sometimes a change in celebrity status is what starts a second career in business. Comedian Joan Rivers is serious about her reasons.
"It was right after my husband's suicide," Rivers said. "And I wasn't getting booked. And I was ice cold in the business. And I had a lot of mouths to feed."
In 1990 QVC, the home shopping channel, approached her about starting a celebrity line. She decided that she might like to try designing jewelry — and Rivers now sells nearly 2 million pieces of jewelry a year on QVC. In the 17 years since her jewelry line began, Rivers has sold more than $500 million worth.
Rivers stays in the public eye with standup performances and her red carpet commentaries on the TV Guide channel. But she says her celebrity only takes her so far in business.
"At this point I don't think the Joan Rivers name means a damn thing," she said. "We have a track record now. It's all about quality. Nobody comes back twice because they like you."
The most important thing, Rivers said, is trust.
"When you see me show you something on television, you can't touch it, you can't feel it," she said. "So I'm really saying, 'I think this watch is fabulous. Trust me.'"
Cohen said people who relate to the star will want to use the products they use. If the star believes in it, they will, too.
Consumers believe in George Foreman. The former heavyweight boxing champion is the most trusted celebrity businessman in America. He's sold more than 70 million of his George Foreman Grills.
"When you go to the airport, sometimes people stop me and say George! We love the grill," Foreman said. "That's greater than them telling me, 'George you did a good job becoming heavyweight champion of the world.'"
Foreman has also added a clothing line at Casual Male to his business empire and even has a "knockout cleaning system."
"My mother told me early, if you learn to sell," he said, "you'll never starve."