alex_tucson said:

The pattern that distinguishes a bad batch from an exit is behaviour rather than product.

No disagreement with alex_tucson. One condition attached. 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.

Ask again with the specifics and you will get a better answer than this one.

alex_tucson said:

The pattern that distinguishes a bad batch from an exit is behaviour rather than product.

I disagree that testing history is decisive. It tells you what a supplier did when they were being watched. Continuity of behaviour under stress — a late shipment, a failed test, a complaint — is more predictive than any run of good results.

Correct me if the detail matters more than I have assumed.

Taking the question as asked, rather than the general version of it. Prices dramatically below market are the strongest single signal, and the reason is arithmetic rather than suspicion. Synthesis, testing, and cold-chain shipping have floors. A price well under the floor means something was skipped, and the two things that get skipped are testing and content.

Happy to go further on any of that.

COA_Karl said:

The useful checklist is about verifiability rather than presentation.

This matches mine closely enough to be worth saying so. One addition: an unstated method makes a report close to uninterpretable. "99% pure" without the technique, the standard and the conditions is a claim, not a measurement.