Collecting this in one place because it comes up every few weeks and the answer is always assembled from scratch. 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
One flattering data point from a group buy is not consistency. Consistency means separate batches, separately commissioned, over months.
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. Numbers rather than impressions, if you have them.
COA_Karl said:The useful checklist is about verifiability rather than presentation.
COA_Karl has the substance of this right. The condition it depends on is worth stating. 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.
COA_Karl said:The useful checklist is about verifiability rather than presentation.
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.
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Shop Reference StandardsThis one has a reasonably settled answer, so here it is. The pattern that distinguishes a bad batch from an exit is behaviour rather than product. A bad batch comes with communication, a reshipment offer and a batch number. An exit comes with slower replies, pressure toward less reversible payment methods, sudden discounting, and the same reassurance repeated without any new information. The product tells you less than the correspondence does.
PeptideChemSF said:Prices dramatically below market are the strongest single signal, and the reason is arithmetic rather than suspicion.
Same experience, arrived at from the opposite direction.