I don't mind giving a special deal to a good customer or the nice ones.
For example, we used to have "The Coffee Club," a bunch of old people that all met up, just to get out of the house and socialize. They usually just had coffee and maybe a snack or desert. Whenever I waited on them, I always gave the coffee for free. They didn't ask for it, but they were always very nice.
However a rude custy who demands a special deal, and yells at the employees who don't even know what she's talking about is a customer I would rather not even set foot in the door.
And what a miserable life they must lead to carry on like that.