You can provide the incentive by frequenting the business. You can provide feedback on poor performance directly to the management. I'm salaried, and no end-user ever can ever give me direct feedback, but they can provide feedback buy buying (or not buying) my companies products. Management then interprets this signal (given many other variables) and takes such actions as makes sense, such as providing incentive rewards or retraining or firing. There's no reason why this model can't work in a restaurant.