From time time I also make the "life is too short" decision. My avocation (see image) has the same issue as well. I would be comfortable saying customers (as well as coaches and players) fire (eject) themselves, I just make it official.
May be a wishful hunch, but it sure seems like I get several orders shortly after a refund, but it is an absolute fact after an ejection, the game is much more fun for all concerned. There is an old saying amongst umpires that the only ejection you regret is one you did not make (I also include those not made soon enough) - same can apply to ending a client relationship.
Might not work for you, but I have a few customers who were close to being fired, but agreed never to write, call, email, fax, or do anything but order each year. I use a similar tactic on the ball field, restricting a coach to the dugout, never to be seen or heard the rest of the game.