While this is a market with demand and supply it is an illegal economy usually run by mafia, corrupt military officials, and other criminals. Those usually involved in the purchase of products are...
Trading in prohibited or restricted products without the consent of the 'authorities'. Illegal buying & selling of goods. Not paying taxes on those products.
Of course you can the whole point of the black market is that it's illegal and when you do get arrested you will be sentenced to a long time so best to get out while you can.