When I do my bartender gig I’m obviously, serving alcohol. Drinking affects various people in different ways, good and bad.
So in that context it really depends on what someone wants to talk with me about, and how they behave in general. Basically I’m always curteous to everyone, and friendly to those who are good natured or interesting. And I’ve had a few fascinating or hilarious conversations that will stay with me for the rest of my life. But I also have regular contact with a few “chatty” customers who are frankly assholes and don’t show or deserve respect.
I guess the best answer to what you’re asking is that I want to put people at ease and make them feel welcome, but I also need to be alert for problems and stay in control. Tending bar may not be exactly like other serving jobs as far as how we engage with the public. Conversation is mostly a tool.