Dr.GutHealth 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.

adam_van said:

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

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 14 orders across 5 vendors: average purity 97.6%, 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.

SarahChen_PharmD said:

I disagree that testing history is decisive.

Coming at SarahChen_PharmD’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.

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

A narrower follow-up, since the general answer is now clear:

What a vetting checklist should actually contain, as opposed to a list of things that are easy to fake?

Closing the loop on my own question.

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.