One of the key points to hit upon is that buying any substance in an illicit manner is a huge risk because you're not getting it from a regulated source like a pharmacist, or whatever. Wherever that product may come from, wherever it may be cultivated or made, there is a huge risk factor with what else could be going into it.
Again, speaking to regulatory factors such as the CDSA and others dealing with such substances, anyone takes a risk when getting something from off the street.