Shawn Achor has become one of the world’s leading experts on the connection between happiness and success. He is the CEO of Good Think Inc. (http://goodthinkinc.com/) where he researches and teaches about positive psychology.
One of the concepts he discusses is how a smile is contagious (I think I remember being told this when I was a child). It turns out that when you smile, it creates changes in your brain (all positive). When you smile at someone else, whether they smile back at your or not, their brain replicates the same responses your brain is having, using “mirror neurons”.
If your business involves face-to-face meetings with your customers, a smile will definitely make someone more interested in doing business with you. Smiling more will actually make you feel happier. Actually, this is a great practice for everyone that you see, whether they’re customers or not.
Just ask yourself: Wouldn’t you rather do business with someone whose presence makes you feel good?