Posting this because the summary going around does not say what the paper says, and the difference matters for how people here are using it.
The useful checklist is about verifiability rather than presentation. Independent test results commissioned by buyers rather than by the seller, consistency across multiple batches over time rather than one flattering report, a physical address and a company registration that resolve, batch and lot numbers on the actual labelling, and a shipping practice that matches what the material needs. Everything a good-looking website provides is cheap to fake; none of the items above are.
Where I think it is weakest: the completion rate deserves as much attention as the headline, because a large effect among those who finished is a different claim from a large effect among those enrolled.
What would genuinely help is knowing how people are distinguishing a supplier having a bad batch from a supplier on the way out. I have searched first, so if this is covered somewhere point me at it and I will read it.
Note on sourcing:
Figures above are from the primary publication rather than the press summary. If a number here disagrees with one you have, post yours and we will work out which of us is reading a secondary source.