This is the version of the explanation I wish somebody had given me, written down before I forget what confused me. It is about vendor vetting, and it is deliberately narrow — everything I am not confident about is marked as such.

What is actually established

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.

The condition it depends on

A caveat about community reputation: it is a lagging indicator. Reports arrive weeks after orders, so a supplier can look excellent for a month after quality has already changed.

The practical version

Red flags, in rough order of how much they should worry you: no verifiable address, no batch numbers, prices far under market, vendor-commissioned tests only, pressure toward irreversible payment, and shipping with no temperature control.

What I am not sure about

What I am after is what a vetting checklist should actually contain, as opposed to a list of things that are easy to fake. I would rather have one careful answer than five confident ones.