PharmD_Rodriguez said:

The useful checklist is about verifiability rather than presentation.

Agreeing with PharmD_Rodriguez, and the qualification matters more than the agreement. 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.

PharmD_Rodriguez 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.

This 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.

Dr.SleepRoch said:

Prices dramatically below market are the strongest single signal, and the reason is arithmetic rather than suspicion.

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.