kate.chem said:

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

Pushing back on kate.chem here. 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.

Worth separating that from vendor vetting, which this thread keeps folding into the same question. They behave differently and the advice does not transfer.

The figures, for anyone assembling their own picture. 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.

BethLabQueen said:

The affordability discussion here usually stops at individual tactics.

Adding the part of the answer the thread has not reached. 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.

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?

Reporting back.

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