Ironically, the thing that’s really gonna fix that is good o’l fashioned capitalism.
Brand recognition is what killed the underground booze trade after prohibition. Brand recognition is what is going to kill underground pot. As a casual consumer of pot, there’s no way I’m gonna take the time to invest in doing research on strains when I’m looking to buy some recreationally, I’m just going to take a name down from a friend who knows what I like and where I can find it. The easier it is to find, the more likely I’m going to be to go buy more.
The illegal trade will slowly die as it becomes more and more inconvenient to buy from it. It’ll stick around for maybe a decade or so after legalization just like bootlegging sources did after prohibition, but long term it won’t last.