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

TrialTracker_MD said:

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

Agreed, with 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.

bbq_ray_KC said:

Eight months with one supplier, then a change in how they communicate that I noticed before I noticed anything about the product.

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

Adding the clinical framing, because it changes how the question reads.

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 16 orders across 4 vendors: average purity 97.0%, zero sterility concerns, 2 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.