The perfect client reads as well as writes. The perfect client has done his or her research on editing and writing, is a good listener, and is willing to pay a professional rate for the professional services requested. The perfect client is diligent about deadlines and schedules and follow through. The perfect client asks thoughtful questions, receives feedback gracefully even when deciding not to listen to it.
And every once in a while, a perfect client will give the editor a recommendation, or write some nice things about the editor in a blog post.
I am very fortunate to have a wonderful list of clients right now. Thank you for your business; it makes work fun.