Maybe by asking them how they are doing, you may be able to gauge better. I know when I'm focused and really busy with any task, I may not smile. It doesn't mean they are not happy. Sometimes we just need to take the time to interact.
Being a waitress is a hard job sometimes. They have to deal with the public and at times this can be hard for those that do not have that ability to just take a few deep breaths and count to 10 and move on. So by us greeting them with a smile and thank you when they pour your drink or take your plates may turn that frown upside down to a smile.
Treat them nicely and they will probably smile at you. You don’t know how many rude people they encounter. (Rude people stink!!)
If people didn't have attitudes towards their waiters/waitresses all the time and showed them a little respect, you would probably receive more smiles. They deal with a lot of people all day! I've even seen the best ones picking up others slack, deal with really bad attitudes, still give their best and they don't get tipped like they deserve...
Smiling, in appreciation that your customers chose to support your employment with their patronage, is part of the job. Without their choice to eat with you, your employment would be irrelevant. if you don't feel that appreciative, you're in the wrong job.
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