Who schedules your appointments?
In the different stores I have run they all had similar problems with filling Saturday's up. You need to be open on Saturday period. Half days do not work. It only helps you that your competition is closed that day. Use that to your advantage and advertise you are the only one open. Things I would do right away.
Do not let the advisors schedule their appointments. Get a scheduler(maybe a cashier) to do it and spiff them on quantity of appointments that show up. If they don't want to be there, they will schedule you to fail without a doubt.
Run a contest with your advisors for the most hrs sold on Saturdays for the month. Make the prize big to start then reduce it later. If they can during a contest month they should be able to do it always.
Keep pushing them to produce. Don't take their excuses. If you do this you will find it will work. You will also find you will not have a problem staffing due to the fact that they are actually making more money than during the week, and doing mostly "gravy" work. Email me with any questions
parnotte@porterauto.com