SarahChen_PharmD said:

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

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.

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

SaraMom3 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…

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 23 orders across 5 vendors: average purity 98.3%, 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.

MikeFit_NJ said:

I disagree that testing history is decisive.

Coming at MikeFit_NJ’s question from a different direction. Order of operations matters more than any single choice here: establish a baseline, change one thing, wait long enough for it to express itself, then measure again under the same conditions.

One thing that is still open after NicoleRaleigh’s answer:

How people are distinguishing a supplier having a bad batch from a supplier on the way out?

Reporting back.

Went back through my own correspondence with an earlier supplier and the warning signs were all there in the replies, weeks before the quality changed. I was reading the product and not the behaviour.