Ever wonder why Costco always checks customer’s receipts as they leave? You’re not alone.

Costco is one of America’s most popular retailers, and the company’s employees are looking to answer specific questions as they check your receipts.

One employee described the thinking behind these last-minute receipt checks to Business Insider. Employees are checking both to make sure you have what you paid for, and that you don’t have anything you didn’t pay for. That much is clear enough, but the company does have specific checks for jewelry and other specific items. Here are some of their guidelines:

• The code at the top and bottom of the receipts are changed daily so that employees know that each receipt was printed on the day of the purchase.
• High-end items valued at over $300 require a supervisor’s initials on them, which employees will check for on the customer’s way out.
• Employees must check the item count on the bottom of the receipt to insure the clerk didn’t under-count or over-count.
• Larger items such as tissue boxes and large bottles have signifiers on the receipt so that employees can look at the bottom of the basket during the customer’s exit.

This may sound like madness to some, but with Costco there is definitely a method behind the madness. Many employees have recounted how this system has prevented the theft of large amounts of Costco’s wholesale goods. For both the consumer and the Costco employee, this system has been proven to work.