Look for a third-party seal.
Third-party seals don't prove a product's efficacy, but they are a good indicator that a supplement has been manufactured properly and actually contains what the label claims. There are a few independent certification organizations, including NSF International, U.S. Pharmacopeia, and ConsumerLab.com, that analyze supplement companies' processes and test their finished products. So spotting the NSF, USP, or CL seal on a label can give you extra assurance that a product has passed strict outside analyses. However, the lack of a seal does not necessarily mean that a supplement is a sham or of poor quality. These programs usually cost the supplement manufacturers big bucks, so many very legitimate companies simply opt not to pursue them.