The big difference, particularly these days, is that your friend's dealer will always do what is in his interest, as will all pot dealers, but government approved ones will be regulated. If your friend's dealer sees his crop has been hit with mould or insects, he'll use whatever he can to save that crop, even if it is very bad for the health of his clients. Government regulation will seek to stop that from happening, as we saw with Mettrum.  That's the only difference that matters, ultimately, and it's one I'll pay a premium for, as I'm sure, most responsible adults will.