Heard about a guy doing insane opsec when selling on the dark web (darknet diaries podcast).
In the end he got busted because a trusted member if his operation got lazy and ignored his rules
Edit: This guy was essentially
Leeching internet via a directional antenna from a neighbour that was significantly away
Not allowing any visitor in with a cell. You had to keep it outside
All drug related actions are done in a cleaned down room.
Tripple sealing dark marketplace orders, wiping everything down with corrosive fluids to destroy any sort of dna material
Not going to the same post office in (I believe 6 months) and only sending of 3-6 shipments at once