Other forms: black markets
A black market is buying and selling in a way that breaks the rules.
Black markets include trade in illicit goods (like selling illegal drugs). But a business selling perfectly legal items or services without following the rules is also a black market. If your state's laws forbid the sale of unpasteurized dairy products, farmers who sell raw milk are operating a black market. This phrase reached the height of its popularity when food and fuel were rationed during World War II, spurring black markets in goods including meat and gasoline.