"Dozens of companies across the country are doing the same thing," bureau spokeswoman Alison Southwick told ABCNews.com. "Maybe they are selling juice instead of supplements, but it's similar kinds of sales practices."
Annual sales of acai products exceeded $15 million last year, up from $500,000 in previous years, according to the bureau. The so-called "super food" has been praised for its antioxidant properties on television shows and on social networking sites, with some claiming it fights cancer, aging and weight gain.
In November, according to the bureau, more than 1.5 million people searched for the term "acai" on Google. Online ads and Web sites often include a photo of a celebrity -- such as Winfrey -- and falsely claim that she endorses the acai as a weight-loss miracle.
While the acai's nutritional benefits have been mentioned on the air frequently, the berry's alleged ability to aid weight loss has often been misconstrued in these ad campaigns, according to the BBB.
Columbia University heart surgeon Dr. Mehmet Oz, who appears on "The Oprah Winfrey Show" as a medical expert, told ABCNews.com that he had never officially endorsed acai.
"Acai is a powerful antioxidant," said Oz. "Colorful, dark foods like red wine, pomegranates, concord grapes, blueberries -- they call them brain berries -- are full of nutrients."
As far as those weight loss properties, Oz said, "I'd be surprised if by itself acai could help."
Harvested as a deep purple pulp from 60-foot palm trees, acai (pronounced "ah-sigh-ee") is exported as a thick pulp and sold in a capsule, powder or juice form at health food stores and online.
Acai products are distributed through such stores as Whole Foods, Wild Oats and Jamba Juice, as well as many conventional grocery chains and the Web.
The berry was virtually unknown outside the United States until 2001, when brothers Ryan and Jeremy Black began to sell acai through Sambazon Inc., promoting its antioxidant properties.
Today billion-dollar beverage giants, including Coca-Cola Co., PepsiCo Inc. and Anheuser-Busch Cos., are adding the fruit to their beverage lineups, according to The Wall Street Journal. It's also found in products from Stonyfield Farm and Haagen-Dazs. Procter & Gamble Co. recently infused acai into its Herbal Essence shampoos and conditioners.
Online, Sambazon sells acai in various forms -- frozen pulp, smoothie, juice, capsules and powder -- but does not offer the "hype" about weight loss or the "free" trial offer.
Although Sambazon does rely on endorsements from some celebrities, like skateboarder Bob Burnquist, the company does not reference either Oprah or Dr. Oz on its Web site.
The company has also been barraged with telephone calls and complaints on its Web site, acai.com, from consumers who have confused Sambazon with companies that use the misleading practices, according to co-founder Ed Nichols.
"All day, every day since this thing started, we've been hearing, 'Please stop charging my credit card now,'" said Nichols. "But when people do reach out to us and say help get us out of this scam, we educate them about our sincere products."
Sambazon stands by its product, which it makes in the company factory in Brazil and ships directly to buyers.
"Anybody can go down to Brazil and buy acai and call a fruit broker, but it spoils almost immediately after picking," he said.
Lauren Cox contributed to this report