Answering the narrow version, because the broad one does not have a single answer. 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.

If somebody has the primary source to hand I would rather cite it than paraphrase it.

DanielChem_CHI said:

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

Right, and one flattering data point from a group buy is not consistency. Consistency means separate batches, separately commissioned, over months.

maya_sedona said:

Six orders from the same supplier over eight months, every one independently tested, and the consistency is the part worth reporting rather than any…

Same position here, arrived at the long way round. 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.

That is the short version; the long version is somebody else's post.

From the other side of the consultation, briefly.

Vendor reputation tracking for vendor vetting: I maintain a personal spreadsheet with every order I've placed — date, vendor, batch number, Janoshik result, personal efficacy assessment (1-5 scale), and any issues.

After 20 orders across 5 vendors: average purity 97.0%, zero sterility concerns, 0 shipping issues (all resolved). This data gives me confidence in my current source and documentation if issues arise.

I encourage everyone to track their orders systematically. Community data aggregation makes us all safer.