After completing 2 intense weeks of back to back projects, at one point - spent two nights away from home, I must say its incredibly satisfying to have both your clients to be truly appreciative.
There is one principle that I live by, which I must say does wonders for business. I ever seek to work in a way that I can say, my God can look at my work and say well done my son, not - you know you could have done much better. So even when I know I have done enough to make the client happy, I can't rest until I know God Himself is also happy with my work. The thing is - He knows my abilities, so even though a client may be happy, God knows if I could have done things better.
Working with the view of God first, it really is powerful. Another thing is, I really believe that my work is somewhat a reflection on my God - perfection was the hallmark of Jesus work, not just in salvation, but also in the carpenter's shop. So I strive to be the best at what I do. The distinction should be clear - when someone receives work from me, it should be seen that a child of God ever seeks to deliver the best work possible.
With that being said, there is true joy one receives from doing good work and it being acknowledged, beside the money, the acknowledgement really makes it worthwhile.