DataDave said:

The useful checklist is about verifiability rather than presentation.

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.

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

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

VendorMark said:

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

There is a second half to this that has not been said yet. Denials are usually procedural rather than clinical, and the order that works reflects that. Get the denial reason in writing, because it names the criterion you failed. Then supply the documentation that criterion asks for — usually documented BMI with a comorbidity, or a failed prior therapy. Then appeal, and ask for a peer-to-peer review, because a prescriber talking to a reviewing clinician resolves a large fraction of denials that written appeals do not. Manufacturer copay assistance is separate and applies mainly to commercial insurance, and patient assistance programmes are means-tested rather than a discount.

OP back with an update, since a thread like this is useless without one.

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.

DebRD_ATL said:

Denials are usually procedural rather than clinical, and the order that works reflects that.

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

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