Also, you can be nice to people without pretending to feel happy all the time, such as by smiling or singing. Being nice could mean efficiently executing their duties.

I'm not sure why talking about emotional labor, smiling and singing, suddenly brought on doubts about decency, niceness, and assholeness in the following reply. I see that as very stressful expectations to have for somebody.

Smiling is a communication of internal feelings. It puts pressure on me as the customer as well when I know my mere presence is an on-button for an emotional act for people. How draining for both parties.