Would you complain in this situation in Marks & Spencer, which is supposed to deliver good customer service;?
You could complain but you were charged the right price in the end, but I would be annoyed if they didn’t listen to me and looked at me like I was stupid- this has happened to me before- where you have to explain the prices to the staff and they argue with you. Just because they work there, doesn’t mean they necessarily know more than you. I would make a complaint, but make it mild and explain that what annoyed you was the attitude of the staff. M&S might take this on board and explain to staff that ‘the customer is always right’, and you might get a good will gesture like a coupon.