This is the exact reason why I choose to carry a professional line of supplements that are GMP certified and 3rd party tested/verified. You want to verify that the product contains the ingredients it lists and in the amount it claims. You also want to verify that the company tests for heavy metals and other contaminants that can harm your health. If you are going to pay for a supplement you better make sure the company proves to you that you are getting what they claim is in that supplement! The purpose adding a nutritional supplement is to improve your health, not harm it.