You charge your clients what you agreed to charge them, regardless of whether there's mistakes later. If you make too many mistakes, you don't make as much money (or even lose money). Therefore, you try not to make mistakes. It's not a miracle, it's normal. Any company that makes a product, as opposed to those selling services, works like this.

Also, allhatnocattle's examples aren't waste, and neither are mistakes. Waste would be paying for a $100/month cell phone plan for an employee that doesn't need or want it, for example. Safeway charging higher prices because people shoplift from them is not waste.