Enough is Enough!
There is a point when it becomes too much to a burden to keep certain clients on. If you’re spending more time resolving unfounded complaints and dealing with problems then actually coaching or supporting, then it may be time to consider ending your agreement with them. You aren’t benefited any by keeping negative people around in your life - and they can be detrimental to your business if you’re spending extra time keeping them happy, detracting from your other responsibilities or clients. Negative clients are often a lot more trouble than they’re worth, weight the benefits and the costs of keeping them on.
There are plenty of good ways to deal with difficult clients, and the tips above should give you a good start. Just remember to maintain your level of professionalism, and you shouldn’t have any problems.