I think we would all agree that humor sells. Just look at television commercials as an example. The ones we remember and don't mind seeing over and over again are the funny ones.
There was a study done a few years ago which looked at the attention and retention of academic content by university students. The results indicated that both retention and attention increased significantly if the professors used humor in their lectures. If these results are accurate, and I believe them to be, they validate my long held belief that if you want to make people listen to you and remember what you said make them laugh.
When you apply this to marketing and sales you realize that the use of humor not only gets your customer's attention, but also helps them recall you and your message long after you have left the scene.
A happy, humorous, smiling company representative is a powerful promotional and selling agent. So hire people with these qualities and train those working for you who don't. Remember a sense of humor is a learned response, it isn't genetic. People are attracted to those with a great sense of humor and a cheerful disposition.