I don't understand how some employment sectors that pay minimum wage, like the restaurant industry, expect the customer to pay  a gratuity for service, whilst others do not. 

Where is the tip jar for the shoe salesperson that sources fourteen pairs of shoes, and then tidies up the mess you leave behind. Or the clothing salsperson that keeps bringing different sizes and different options into the change room for you, and has to untangle the inside out on the floor mess when you leave.

All of these service sectors pay minimum wage. And yet one of these things is not  like the other. Why.