It's hard to win when you're working in customer service. If you are casual and approachable, people think you're unprofessional and careless. If you ask several clarifying questions and maintain a "professional" manner, people think you are trying too hard and seem unfriendly. There is literally no way to win, so you have to gauge what vibe to have with each customer individually, which can be very taxing, especially if you work in a busy fast-food restaurant where customers will treat you however they want. Mean customers usually just want somebody to blame for their bad behavior in public, and low-paid employees are an easy target.
One Newcastle resident recently had such a bad day that he decided to tattle on a Greggs employee for using a greeting he deemed too casual. While I am not British and don't exactly understand what he meant by, "Morning mate, what you have having," I know it was not cause for tweeting the official Greggs Twitter account.