“So they finally legalize it and you trying to say they’re purchasing illegally grown pot and selling it through legal retail shops. You have evidence of this taking place?”
http://www.slate.com/articles/news_and_politics/altered_state/2014/01/colorado_marijuana_legalization_how_lucrative_is_it_to_be_a_legal_weed_dealer.html
Your link doesn't say they’re purchasing illegally grown pot and selling it through legal retail shops. Here's what it does say:
"CT does not have to pay licensing fees, taxes, or other regulatory expenses. Over the past few years he’s dropped his rate for an eighth from around $50 to $30 to meet or beat the going price at Colorado dispensaries"
In other words: legal pot is cutting into illegal profit margins, and lightly taxed and regulated will do so even more.