Well i probably should have mentioned that this is going down in a restraunt so they wont be coming back for a refund
If it's a chain/corporately owned restaurant you'll get caught pretty quick since there are accountants that sift the statistics pretty thoroughly. Accountant = someone who can do simple math and balance a checkbook, and other middleschool level math.
If it's an independent affair, uhm, one in a hundred servers can balance their paperwork correctly at the end of a night, and the ones picked to be managers aren't picked for their math skillz. Owner/operators are classically fools floating on parental or drug money, and even if they purchase a top of the line POS system that gives them all pertinent sales trends and statistics they are ultimately innumerate fools who don't know how to interpret numbers.
Owner: "Joseph, your weekly sales are 75% that of the other servers. You need to work on that or we'll have to let you go."
Me: "I'm only scheduled three days per week and everyone else is scheduled five days. That means I am here 60% as much as they are, so to net 75% of their sales means I am selling more per hour on the floor than they are. Further, I've left early at least one night a week for the last couple months because everything's been slow, which means my per-hour sales are through the roof compared to anyone else on the floor."
Owner (huffy): "That's not how it works."
Me: "Then why does that report you're holding also show that I have the highest per head and per table sales of anyone on staff? Look, down here it shows my per-hour sales and it's quite a bit higher than everyone else's."
The dildo would walk away mumbling to himself angrily, and then be back two weeks later with the exact same horseshit. It's not that he personally wanted me gone - he had no problem firing anyone for petty reasons - he was honestly that stupid.