carson's image was front and center on mannatech's website and promotional material. >> this is ray robins with the platinum group. we are proud to be the exclusive sponsors of the program you're about to watch with dr. ben carson. >> reporter: distributors calling them sevens the platinum group and signed on to underwrite ben carson's public television special. cnn spoke with three former sales and marketing insiders with mannatech that say the involvement but the neurosurgeon went a lodge way toward legitimizing a product were scientific committee was calling worthless. >> a neuro scientist is something the company wanted on their side, on their team to grow the company in a very legitimate way. >> reporter: it's obvious why mannatech wanted a highly respected neurosurgeon to speak highly of the product. what is not obvious, why a neurosurgeon would lead his name to an unproven product. we asked about that at johns hopkins where ben carson became a famous neurosurgeon. >> we here at a major medical and bio medical research institution have a special responsibility to abide by evidence and share evidence based, knowledge with people.