DataDave said:The pattern that distinguishes a bad batch from an exit is behaviour rather than product.
Pushing back on DataDave here. Import rules are jurisdiction-specific and this board keeps giving US-shaped answers to non-US questions. What is a personal-import allowance in one country is a controlled-import offence in another.
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.
Dr.SleepRoch said:Import rules are jurisdiction-specific and this board keeps giving US-shaped answers to non-US questions.
Adding the part of the answer the thread has not reached. The useful checklist is about verifiability rather than presentation. Independent test results commissioned by buyers rather than by the seller, consistency across multiple batches over time rather than one flattering report, a physical address and a company registration that resolve, batch and lot numbers on the actual labelling, and a shipping practice that matches what the material needs. Everything a good-looking website provides is cheap to fake; none of the items above are.
Worth separating that from vendor vetting, which this thread keeps folding into the same question. They behave differently and the advice does not transfer.
If somebody has the primary source to hand I would rather cite it than paraphrase it.
Trusted third-party HPLC & mass spectrometry analysis. Verify peptide purity with the lab the community relies on. Independent. Accurate. Transparent.
Verify Your PeptidesEst. 1998. The synthesis house behind the vials you send for testing. ISO 9001 and cGMP certified, 1,500+ staff, batch-specific COA with every order.
Browse GL BiochemOne thing that is still open after stefan_berlin’s answer:
How people are distinguishing a supplier having a bad batch from a supplier on the way out?
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.