When I was a teen, I used to work at a high end local grocery store. We were paid more than our peers at other stores, the stores were always clean, the managers tried to be nice and helped us out with bagging and cleaning when necessary. We were expected to be cheerful to customers, limit private conversations between workers (it’s super rude to chat with your coworker and ignore the customer buying $200 worth of groceries), and keep our uniforms clean and presentable. I’m a pretty serious introvert, and (due to chronic illness) was in a moderate amount of physical pain during the time I worked there, but I really didn’t find it that difficult to be cheerful to customers. Most interactions were brief, and the managers didn’t expect us to behave like Disney princesses, just friendly/helpful people who were paid to assist customers.