black market

nouns

people who engage in illicit trade
is a type of (narrower)
the customers for a particular product or service
"before they publish any book they try to determine the size of the market for it"
an illegal market in which goods or currencies are bought and sold in violation of rationing or controls
is a type of (narrower)
the world of commercial activity where goods and services are bought and sold
"without competition there would be no market"; "they were driven from the marketplace"

verbs

deal in illegally, such as arms or liquor