The old snake oil salesmen are alive and well and now dwell in the diet supplement industry. There is just so little evidence that most of them offer any benefits with some exceptions when diet supplementation is necessary for medical reasons. Regulation appears to be almost impossible unless consumers demand it; however, that is also unlikely. Many people do not favor giving up their often useless supplements even when they know the facts. It shows the power of the placebo on which most of them (the supplements) operate.
See a previous post from 2012 HERE.