NurseKim_ATL said:

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

This is where I part company with the consensus forming above. 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.

Adding the numbers, since they settle part of this. 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.

LipidDoc_ATL said:

The affordability discussion here usually stops at individual tactics.

Coming at LipidDoc_ATL’s question from a different direction. 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.

Following on from pete_manc_UK — 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.

Follow-up — getting the denial reason in writing was the step that mattered. It named the criterion, and the criterion was a document I already had.