As the above ground businesses are taxed / regulated out of existence or forced to migrate elsewhere, the Black Market Grows.
The article linked at the top assures us that the underground economy is the second largest economy, with a GDP well in excess of 10 trillion dollars yearly.
A map at the site displays the portion of economies around the world which are underground. A new euphemism for black markets, System D, for debrouillard, has been coined by Robert Neuworth, to convey his impression of the self reliant sorts of people who make their living in the black markets. Excluding gun running, drugs, and slavery, Neuwirth does not see an inherent moral problem with the underground economy.