I agree to disagree. I totally agree with what you are saying about the lack of self respect that you may be exhibiting by allowing somebody to disrupt your meeting and time that you may need to discuss matters with other potential and existing clients. I say, "if the guy is not happy with the service you are providing him, and it was meeting all of his needs, then it is time to stop wasting your money and move on!!" You simply tell the client that there must be a disconnect somewhere between past conversations you have had with each other, and until you can find it and come back with a solution for him, you feel more comfortable if you two just part ways, but leave him a name or two of somebody you would refer him to.  this way if you do find a solution that was not working before, but you feel confident now that it will, it might not be as painful in trying to win him back.

on the other side of the ticket, there are those who are in charge and they have a hard time going face to face with confrontation, and will totally ignore a problem, in hopes that it will go away on its own.