Its common sense that people like to feel appreciated. A simple thank you goes a long way in maintaining a relationship. When you have business to conduct, its so much more important. As marketers the need to make their clients and customers feel appreciated. This appreciation has to feel genuine.
In 2012, I was introduced to SendOutCards, an online gift and greeting card company. I had helped a friend get his website up and running. A few days later, I received a thank-you card with my name printed inside in the message. I remember feeling really appreciated. I call this feeling the "Greeting Card Effect."