If there's one vendor I'd trust over any others it's Nootropics Depot. They do all their testing in-house, because it is much more reliable than 3rd party lab testing. The owner frequently gives extensive insight into how the supply chains and testing work. Recent example: https://old.reddit.com/r/Nootropics/comments/cength/testing_...

There's stores like The Vitamin Shoppe, where you're going to get genuine products. Some manufacturers use labs such as USP to assure you're getting what you pay for. So, if you buy products with lab seals from reputable shops, you're probably safe.