Because chemical analysis is a solved problem, peptide synthesis is commercially trivial, and black market sellers live and die by their reputation. Additional

Because chemical analysis is a solved problem, peptide synthesis is commercially trivial, and black market sellers live and die by their reputation. Additionally, grey-market supply is guaranteed to be real, because anyone can sell it for nonpatented use cases and there will be a huge demand by researchers for it, as biochemists don't often do their own peptide synthesis.