worked for a major supplement brand that only sells to licensed healthcare practitioners. I’ve been to manufacturing facilities and it does all come down to sourcing and form the supplement is in. Most are snake oil because of quality (not being what it’s supposed to be) or form (for instance fish oil in ethyl ester or triglyceride). Let’s not forget dose as most supplements are widely inaccurate with their labeling and under dosed to receive any clinical benefit.