Dr.NateNeph said:

Prices dramatically below market are the strongest single signal, and the reason is arithmetic rather than suspicion.

I read this differently from Dr.NateNeph, on substance rather than tone. The affordability discussion here usually stops at individual tactics. At list price this class is out of reach for most of the people who would benefit, and no amount of appeal strategy changes that — it is a pricing problem wearing a paperwork costume.

One concrete data point for the thread. Red flags, in rough order of how much they should worry you: no verifiable address, no batch numbers, prices far under market, vendor-commissioned tests only, pressure toward irreversible payment, and shipping with no temperature control.

Dr.GastroMayo said:

The affordability discussion here usually stops at individual tactics.

There is a second half to this that has not been said yet. 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.

One thing that is still open after Dr.EndoIndy’s answer:

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

Closing the loop on my own question.

Update: approved on the third attempt after a peer-to-peer. Nothing about my case changed; only who was doing the talking.