Heavily agreed. The supplement industry has such a low level of reliability that it has really soured me on so many practices people have. And I flat out do not understand how some of the supplement stores survive.
“There's a sucker born every minute.”
I think mostly through placebo effect, people buy a supplement to treat condition X and they think it's getting better, so they keep buying.
I mean, just look at the wide variety of homeopathic "cures" that are often so diluted that there might not be any molecules of the active ingredient left. Yet people keep buying it.