This review is of the "USP Verified Dietary Supplements" page, which you can reach directly at www.usp.org/USPVerified/dietarySupplements/supplements.html.

We all want to be sure the nutritional supplements we buy are acceptably pure and potent. To this end some shell out $33 a year to ConsumerLab.com for results of its periodic surveys. In most cases, however, a wiser course is to get completely reliable information here at no charge, from the venerable U.S. Pharmacopoeia. A plus is that you can also find out where to buy the listed products.

(It's true that USP charges the companies for its seal. The fact is, however, that some very inexpensive brands, e.g. Nature Made and Kirkland Signature, carry the USP seal.)