CashBack Hassles

Why is it such a hassle to receive CashBack at the till? The moment you start saying that you would like CashBack the person helping you immediately turns sour on their faces. Shoprite why do you offer a service that is such a hassle for a customer to receive because of your employees. FNB even sends me SMS messages encouraging me to get Cash at the till but most of the time I am told there is no money and even start queueing at another till. Shoprite praises itself for offering a wide range of services for shopping convenience but the manner in which the services are executed by most of it's employees that I have engaged with is PATHETIC!!