While I understand you feel it relaxes people, I sure hope you're from the south or somewhere where using endearments on strangers is considered appropriate. I assume that if you are not, you would be smart enough to adjust accordingly. My dad was in the hospital recently and got called sweetheart by a nurse and was LIVID! To him, it was a condesending insult and, since he was lying helpless in a hospital bed, he did not handle it well. Put it this way, a feeble old man doesn't want to be called one. Seriously, it was a setback for him and could have had horrible consequences for his health.
Could you please explain how being called a name (expecially a term of endearment) could result in a setback or horrible consequences for his health.
Lord help, this is why I don't work with the public.

I mean, it might be a bit informal, but I never knew some people took offense to it! I was a lot more careful after that.
There was a guy that I went off on one time because he made some pssst pssst sound at me when I walked by and I had to explain to him that that is not the way to get my attention. I think he was shocked that I said something but his friends were laughing at him.