I have a season ticket. My local chemist knows my face as as I'm there every couple of weeks minimum. If I go somewhere else, though, I'm not always asked to show my card, it's true. That usually just means a lazy or untrained sales assistant, and you see them in shops everywhere. (Not talking about Dot Hawkes, of course.)
As to whether I should pay - well, I take 400mg of allopurinol a day. But they don't make them in 400mg tablets so I have to buy 300mg + 100mg, and pay for two prescriptions. If you're in that sort of position, I can understand why you might feel a bit resentful about the charges.