Working with Incompetence

My job is easy and by easy I mean I can usually count on at least 2 hours a day with absolutely nothing to do. It is for that reason that I get so angry when I come in to work and the girls that have worked the day before me have left whole boxes of things that haven't been put away. Mostly their excuse is that they were too busy. I know that this is a lie. I know this because there is a program on our computer that shows how much sales were done the day before and also how much sales each associate has rung up and guess what, I'm the highest seller. If I'm the highest seller and my days are consistently more busy than the other days and I still have hours of free time then I know the other girls have plenty of time to get the job done. How annoying!