That is one of the most difficult questions that any mobile operator must ask. However, the problem you are having is wanting to make sure you get ever possible customer, this is where you are making the mistake. If your business is growing day to day, look at the growth % and then add that to yesterdays number to get today's. If business booms that day and you sell out early, pack it up and go home and instead of feeling depressed that you could have done more, congratulate yourself on selling out early and having a great day!

Be careful, it is possible to have certain days with lower or higher growth than others, so Monday's sales might not be more than Sunday's but they might be higher than last Monday's if that makes any sense to you!

Hope this helps!