PlumpRump:
I was more referring to the kid down the street selling dope. It just wouldn't be profitable to sell something that is already legal. It would basically be like someone trying to sell "black market" beer or something similar. It just would be a waste of time.
Commercialized weed will most likely have regulated potency levels which will most likely be set artificially low. Let's say 8% potency. Well, the innovative and business savvy black market dealers/growers will offer 25%+ potency (as they already do). With so many different types of strains already in existence, the opportunity for specialty boutique niches is prosperous. So, if one considers that most people will prefer the convenience of buying weed rather than go through the hassles of growing their own, the black market will remain profitable. The competition between the two markets will provide for a good checks-&-balance system.