A Certificate of Analysis is a laboratory report that pins quality claims to a specific batch of material - not to a product line, not to a brand, but to the exact lot inside the vial you are being asked to pay for. On Peptide Exchange, every active listing is gated in code on a batch-matched COA before it is allowed to go live.
The two lines researchers should look at first are the HPLC purity result and the mass-spectrometry identity confirmation. Purity tells you what fraction of the sample is the claimed peptide. Identity tells you that the main peak is actually the molecule you ordered - a high-purity result for the wrong compound is still worthless in the lab.
Finally, check the method and the test date. A COA from an accredited lab, run on the same batch, and no older than the material's documented shelf life, is the difference between a verifiable batch and a document that merely looks official.