e. The firm’s product has few substitutes.
This information best refutes the claim that the firm is using illegal methods to earn monopoly profits. If the firm's product has few substitutes, it means that consumers have limited alternative options to switch to, even if the firm were to increase its prices due to its monopoly position. This lack of substitutes reduces the competitive pressure on the firm and makes it less likely that it needs to resort to illegal methods to maintain its profits.