RetaRick_CA 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.

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

sarah_TO said:

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

Shipping damage protocol for vendor vetting orders: if your package arrives with visible damage, temperature excursion, or broken vials:

• Photograph EVERYTHING before discarding packaging
• Note the temperature of the cold pack (liquid = possibly too warm)
• Contact the vendor within 24 hours with photos
• Request a replacement shipment or refund
• Do NOT use potentially compromised medication

Reputable vendors will replace damaged shipments without argument. If they push back, that's a red flag about the vendor.

Dr.SurgeonPGH said:

I disagree that testing history is decisive.

Adding the part of the answer the thread has not reached. It helps to ask what evidence would change your mind before you look at any. If nothing would, the discussion is not about evidence, and it is better to say so early than to spend nine posts discovering it.

Following on from Dr.BariatricHTX — and this may be the naive question:

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.