In general, monopolists charge a higher markup when customers have which type of substitutes?

Monopolists typically charge a higher markup when customers have few good substitutes available. The reason for this is rooted in the concepts of price elasticity and market power. When a monopolist faces a situation where there are limited alternatives for consumers, it means that the demand for their product is less elastic. This means that consumers are less sensitive to price changes; they are more likely to continue purchasing the product even if the price increases.

With few good substitutes, the monopolist can increase prices without losing many customers because consumers do not have viable alternatives to turn to. This ability to raise prices leads to higher markups, as the monopolist capitalizes on their market power to maximize profits. Conversely, if there were many good substitutes available, the price elasticity of demand would be higher, causing the monopolist to keep prices lower to remain competitive and retain customers.