An article from Journal of American Medical Association in 2017 evaluated CBD products to assess labeling accuracy of CBD products.  84 CBD products from 31 online CBD companies were purchased and analyzed.  This study evaluated many products to allow proper sampling and ensure adequate representation from many different available products. 

Among CBD products purchased online, a wide range of CBD concentrations was found, consistent with the lack of an accepted dose. Of tested products, 26% contained less CBD than labeled, which could negate any potential clinical response.

This study exemplifies the reason to obtain lab results or certificate of analysis when purchasing CBD. 

JAMA 2017-Labeling Accuracy of Cannabidiol Extracts Sold Online