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
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.
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. Tell me what I have not thought of.
sarah_nash92 said:Prices dramatically below market are the strongest single signal, and the reason is arithmetic rather than suspicion.
That is correct as far as it goes, and here is where it stops going. 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.
sarah_nash92 said:Prices dramatically below market are the strongest single signal, and the reason is arithmetic rather than suspicion.
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.
Sigma-Aldrich — Research-Grade Standards
Certified reference materials, analytical reagents, and research-grade standards for peptide verification. Trusted by laboratories worldwide.
Shop Reference StandardsThis one has a reasonably settled answer, so here it is. 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.
DataDave said:The pattern that distinguishes a bad batch from an exit is behaviour rather than product.
Agreed, and mass spec answers a question purity does not: identity. High purity tells you one thing dominates the chromatogram, not that it is the molecule you ordered. A mass within about a dalton of expected is the identity check.