The OP pivoted to restaurant service. In this case, I'm paying for the experience of nice meal. Having a pleasant server is part of that experience. Nobody has a perfect day, everyday, but someone performing this kind of service should genuinely enjoy serving people. If the server actually disdains helping (non-asshole) diners have a good meal, then they probably shouldn't be working in a restaurant. There should be no need to fake friendliness, hire friendly people.