Clients Are Like Children You Don't Hug
I know the title is way over the top but bear with me.
In the beginning, clients start off being happy with your good work. When I say, "Your good work", I mean you as a company. However, after you exceed their expectations a few times they become happy and comfortable with you, the person.
The business-to-business relationship begins because of surface-y things: A good reputation, word of mouth, etc. Long-term the client begins to develop a deeper connection secured by trust and dependence. And who can blame them? You make their problems go away. Sometimes magically.
As you grow and become busier you have less and less time to spend with each client. If you get big enough, you may have to put someone else from your company in touch with them — hopefully someone as conscientious and service oriented as yourself. When you do, remember that the client doesn't give a rat's ass how great the new person is. They want you.
Your client can be the coolest, most rational and mature professional in the world, but when you pull the switch-a-roo be prepared to nurture them through a little pouting. And make sure your new guy has their best interest in mind, pays them some respect and gives super-human service.
Just sharing an observation. I'm not that big, yet, by the way.