Final answer:
In both monopolies and monopolistic competition, firms act as price makers, having some control over the prices of their products. Monopolies control prices due to lack of competition, while firms in monopolistic competition can influence prices through product differentiation.
Step-by-step explanation:
A similarity between monopoly and monopolistic competition is that sellers are price makers rather than price takers. In both market structures, firms have some control over the prices they set for their products. A monopoly is characterized by a single supplier with exclusive control over a market, which allows them to manipulate prices. Monopolistic competition, on the other hand, has many firms competing with similar but differentiated products, allowing each firm to have a degree of pricing power over its unique offering. Strategic interactions among sellers are more characteristic of oligopolistic markets, and a small number of sellers is a trait of an oligopoly rather than monopolistic competition.