it varies, they aren't required to be friendly in general but there is a certain pressure on the customer because if you don't say anything you're treating them like "the help". waiters at more expensive restaurants are more attentive. they just don't do the cringy "hiiiiii welcome to goy's slophouse our special today is reconstituted wheat sticks with petroleum-based cheese, do you like the badges i pinned to my uniform? xd"
United Kingdom