Darknet marketplaces are selling Covid-19 vaccines for $250 to $1,200

You could do reverse transcription and sequencing to confirm the presence of the full length spike protein. That should tell you with pretty high confidence that it’s authentic. But the really interesting “biopunk novel plot” future would be some sophisticated counterfeiter who is actually producing the correct mRNA sequence and packaging it in LNPs. If the counterfeiter was able to charge a thousand dollars per dose, it could be quite profitable even at small scale.