In fact, an exclusive dealing contract often contains a "penalty clause:" After signing the contract, if the consumer still wants to buy from other firms, he can do so by paying a penalty to the monopoly firm. In this case, of course, he also needs to pay the actual seller.

Suppose that Firm C modifies the contract offer to the consumer: There is no sign-up bonus, and its price is p^c. If, after signing the contract, the consumer wants to buy from other firms, he needs to pay Firm C an amount of d. Other aspects of the game remain the same.