A retailer may boost demand for a manufacturer's product through unobservable promotional efforts. Fixed fees cannot be used to freely allocate profit within the vertical structure. When manufacturers have market power, the equilibrium wholesale contract features a retail price below cost together with a rebate for incremental units bought by the retailer when effort has succeeded in boosting sales. Loss leading emerges as an incentive device in such an incomplete contracting scenario. A ban on below-cost pricing leads to a higher retail price and a lower promotional effort.