It's more about customer service. Make your customers happy and they will keep coming back. Upset them and you lose a customer forever. And, you will hear more from one unhappy customer than 100 happy ones.
In my experience the retailer rarely hears from a customer they upset, but loads of former potential customers do. Its even rarer for a satisfied customer to tell someone else they had good service.
A LDS offered free fills during their open day. I took in three cylinders and the guy (brought in for the event) said its only one that's in the T&Cs. But I explained there were no T&Cs in their Facebook promotion, but he insisted. Fine, I went else were for my fills and also spend £200 on other things.
Interestingly, later that day the shop manager phoned me and apologised as the T&Cs had not been posted on FB. He offered me 15 fills in compensation.