Opening up Sundays will actually hurt sales! When they were closed on Saturdays AND Sundays, sales were up. People liked to go to dealerships on weekends and not be bothered by salespeople and then take time off (or come in on Mon-Wed-Thurs evenings) and buy their car. Being in the car sales business for over fifty year, I've made quite a study of it. The Detroit dealers are closed on Saturday AND Sunday - they agree with this plan!