I've researched trustworthy brands a lot, the ones I settled on are Nootropics Depot, Viva Naturals and Nordic Naturals. I prefer those with only Vit E as preservative.
- Viva Naturals from recommendations and testing (Labdoor)
- Nordic Naturals is a well-known premium brand
frankly I haven't documented, these are just some things out of the top my head