Not all supplements are created equal. It's often difficult to gauge a product's quality after using it, but most especially before. I've always looked for reviews online before pulling the trigger. The Amazon reviews are helpful but not backed by actual lab results. I finally found a 3rd party site that tests the purity and accuracy of 15+ main stream supplements (protein, probiotics, fish oil, multi vitamin, vitamin D, calcium, BCAA, creatine, etc..) and ranks them based on either quality or overall value. This site is especially helpful for narrowing down the contenders for supplements that companies are known to exaggerate their content/quality like fish oil, probiotics, and protein. Hopefully this helps some of you guys narrow down your search.
https://labdoor.com/ (no affiliation)
https://labdoor.com/ (no affiliation)