Market price is the main approach that the economy as a science employs as an indicator of scarcity or abundance of supply or demand in every market. The problem appears when price is manipulated by one side of the market, when price loses its status as an indicator, which means the market doesn't work freely. This is due to the fact that we lose the right information about each market in question. Market price has given rise to a lot of written opinions since scholastics’ just price, amongst them that of Adam Smith, who in 1776 wrote about the difference between price of competition and monopoly price:

Economists are looking for a way to demonstrate which price has been reached in a competitive market and is, therefore, fair, and which price responds to a monopolistic market because suppliers are getting extra profits due to market control. The idea is not difficult to understand, indeed, the difficulty lies in demonstrating who are the agents and how they are controlling the market.