Black market is a nomenclature for the sale of products beyond the recommended price.
For example in Nigeria, government regulates the price for the sale of petroleum products and there is an expected margin practitioners are expected to make from their investment.
The logic behind government interference in the market system is to make some basic good available to the public.
By setting prices, producers cannot charge beyond the ceiling fixed by government.
Consequently , any sale beyond the prices fixed by government is regarded as a black market and it is contingent upon excess demand as a result buyers are prepared to pay a higher price for procuring more quantity of the goods and sellers are equally excited to sell beyond the ceiling price as this brings more profits.