Thank you for the excellent article, Michael.
My wife told me about a training session for bank tellers in which they had a mirror set beside the phone and you were supposed to smile while talking on the phone. The idea was to make sure you remembered that you were talking to a real person and potentially a client.
I think this is probably good advice - and may even work when writing e-mails or other correspondence. I try to picture my clients in front of me when I am responding in any format so that I don't just look at "text."
I agree that smiling insincerely is not going to work very well. Usually clients pick up on this from a mile away and probably wish the person was more honest - even it it means a little disgruntled or unhappy.
(Granted there is that old saying "fake it until you make it")
It isn't always easy to remain calm and cheerful with difficult clients. I would suggest trying your best to understand their fears, concerns, etc. However, if they are too difficult, I have no problem letting a client go (a very rare occasion - and generally they become far more genial when this is suggested!).
You have made some excellent points /reminders for all of us.