The quality of your supplements, herbs and homeopathics (holistic medicines) is important. I generally don’t recommend purchasing these items from the typical grocery store, drug store, Amazon or Ebay. Good quality products may be expensive. Lesser priced similar items may be imitations and the labels may not reflect the contents. See here and here.
I recommend that my patients look for products in reputable health food stores, doctor recommended sites, and/ or websites from companies they have researched and are satisfied with their quality control. Along with some local health food stores, I trust and typically use these two following sites for holistic medicines and products: