Black seed oil has been clinically proven to kill candida. And, as a type II diabetic and someone who's struggled with her share of candida growth, I know what has worked for me; ingesting black seed, black seed oil, using it in my vaginal douches, to combat yeast infections, and also eating a diet free of the starches and sugars that candida thrives on.
Hawking their wares? I can't speak for anyone else, but this has worked for me, and I'm a firm believer in using black seed to fight all manner of disease. So, if the cure is in the colon as you assert, then using the oil in an enema should help.