Finding & Keeping Quality Clients

I conduct events called Conversations that Matter. Over the last six months I have gathered entrepreneurs together to engage in dialogue over issues that impact them directly.In every group, no matter which city I am in (Cape Town, PE, Durbs or Joburg) the same issues come up. How do I find QUALITY CLIENTS - but not only this HOW DO I KEEP THEM? I wanted to get your opinions on this one?

So let's start here...
a) How would you define a quality client
b) How does one find quality clients?
c) How does one keep quality clients?

Look forward to hearing from you!