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.
One thing that is still open after Dr.GastroMayo’s answer:
How people are distinguishing a supplier having a bad batch from a supplier on the way out?
quinn_sf said:Red flags, in rough order of how much they should worry you: no verifiable address, no batch numbers, prices far under market, vendor-commissioned…
There is a second half to this that has not been said yet. 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.
Ask again with the specifics and you will get a better answer than this one.
Certified reference materials, analytical reagents, and research-grade standards for peptide verification. Trusted by laboratories worldwide.
Shop Reference StandardsClosing the loop on my own question.
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.
PeptideChemSF said:The useful checklist is about verifiability rather than presentation.
Right, and one flattering data point from a group buy is not consistency. Consistency means separate batches, separately commissioned, over months.
Worth separating that from vendor vetting, which this thread keeps folding into the same question. They behave differently and the advice does not transfer.