I recently encountered a similar situation in a local NYC restaurant. I accompanied a friend to a restaurant in his neighborhood. During the meal, the waitress forgot to add one item to the bill.

As we were getting ready to go to the cashier to pay, I said to my friend that we could simply tell the owner and our bill could then be corrected (upwards).

My friend told me that the owners of the restaurant were very strict with the employees, and treated them harshly. If we pointed out the mistake, the owners would likely suspect that the employee was deliberately giving away food to friends and strangers alike. Our innocent pointing out of an error in the bill would likely be seen as denouncing the employee.

At that point, I kept quiet. We paid the bill, and departed. I felt comfortable not giving the owners any ammunition to use in badgering a hard working employee.

Sometimes, silence is best.