Two separate rating systems run on this site, and they measure different things. Conflating them is the most common way to misread a page here.
The evidence grade applies to compounds and describes the strength of the human evidence only. A is an FDA-approved medication with strong human clinical data. B is meaningful human clinical data supporting efficacy. C is early human trials or a mixed, unsettled literature. D is animal and preclinical data only. E and F are weaker still, down to mostly anecdotal or unsupported claims. A high grade is not a recommendation and a low grade is not a verdict that something does not work — it means nobody has shown that it does, in humans, yet.
Vendor assessment is built from records rather than reviews, because reviews of anonymous sellers of unregulated products are the least reliable input available. The strongest signal is third-party purity testing: an independent analytical lab assays a specific lot and issues a certificate reporting measured purity. Where a vendor's advertised purity and its median measured purity disagree, both numbers are published side by side with the assay count.
Alongside assays, vendor pages record FDA warning-letter history, whether the storefront is reachable and independently verifiable, and the vendor's own stated ordering, shipping and returns terms — each fact attributed to the page it was read from, so it can be checked or disputed.
The limits are worth stating plainly. An assay describes the lot submitted and nothing else; it is not a guarantee about a later batch. Purity is not identity — a sample can assay clean and still be the wrong compound or the wrong concentration. A vendor with no assay data has not been tested, which is not the same as having failed. And a vendor can be accurately described here and still be selling something you should not take.
Where the data does not support a page, the page is kept out of the search index rather than padded. That is enforced in the build itself: any page whose crawlable body falls below a set length is held back automatically.
Related: Peptide library, Vendor directory, Independent lab tests.