If a seller of goods refuses to sell at the agreed price, the buyer may purchase substitute goods and recover the difference between the cost of the substitute and the contract price. When a seller of services fails to provide services, the measure of damages is the reasonable cost of replacing those services. When a buyer of services fails to pay for the services provided, the measure of damages is the agreed contract price for the services. Various defenses are available which may reduce the eventual recovery. The plaintiff must prove losses of net profits, not gross profits.
Net profits are gross receipts minus expenses.
Proving lost profits with precision is difficult. However, mathematical exactitude is not required. What that is will vary from case to case. Davis v. Small Business Inv. Evidence that plaintiff has lost business income or business opportunities is not enough by itself.