What you describe is how it worked for my first set of customers. I solved the needs of the first person, and then for each subsequent customer, I was introduced by the previous one, met with them, and had a 'be myself' approach. There has never been any paperwork beyond a simple text file describing the work that will be done, and no one has ever signed a piece of paper. I just showed what I did for the previous guy and I believe they liked the fact that I wasn't really pushing a product, I just knew how to develop something that solved a problem for them. I am very comfortable with this approach and perhaps I shouldn't change it.
However, pretty soon I will have exhausted the potential clients in my local area since it's not a huge niche. My thoughts were that some other organizations might have different attitudes towards forking over a lot of money to one guy in blue jeans, and that maybe I would benefit from actually "learning" sales. This thought came from watching this particular interview:
http://mixergy.com/maponics-darrin-clement/
He focuses on a mapping niche, and describes how he was able to expand and sell more expensive software by actually taking formal sales classes.
I really would prefer not to do this and would prefer to just say "check out what I did for these other folks", but then again I'm willing to do what it takes.