Quick reference since this comes up constantly. If you want to verify what's actually in a vial rather than trusting the seller's COA, here's the basic process:
Pick a lab. The commonly used independent ones are Janoshik, Chromate, and Freedom Diagnostics. Each has slightly different submission steps and pricing (~$50–100 per sample depending on the test).
Order the test on the lab's site first — you'll usually get a submission ID or form.
Send a sealed vial (or the requested amount) per their instructions. Don't reconstitute unless they ask.
Results come back as an HPLC purity figure, often with a chromatogram and sometimes mass spec for identity.
Two things worth knowing: a purity number tells you how much of the target compound is there, but identity testing (mass spec) tells you it's the right compound — those are different questions. And one test is a snapshot of one vial from one batch, not a permanent verdict on a shop.
If anyone's tested recently, what lab did you use and how was the turnaround?