Greedy intent by Shell franchisees- Shell Edwin Swales Durban

I had the worst experience ever at the Shell convenience store on Edwin Swales Durban (the smaller one). The cashier refused to let me swipe for a R7 packet of chips. They said I can only only swipe for R20 or more. I had a pregnant wife in the car who wanted those chips. The difference is that whether it was R7 or R20, the franchisee would still have to pay the same percentage commission on the speedpoint (roughly 1.9% depending on the agreement with the speedpoint provider). With that being said, I believe that the franchisee acts with greedy intent. I had no cash on me to buy the chips so I left the convenience store.