I have only had to do it a few times.
One client would complain 3 weeks after her highlights were done that they werent close enough to the roots. I would offer a redo which she would book in 2 weeks time. In the end I worked out that she was paying for 2 full heads per year! cheeky cow!! As I am highlighter-in-cheif of Chislehurst, with no other clients complaining, I told her to sling her hook.(my highlights grow out of the head by the way)
Another client was in OK magazine, she then got it into her head that she should book me every morning in case she went anywhere she might get "papped". Most of these appointments got cancelled at the last minute, which was a waste of my time and money. I refused to book her and she threw a wobbly (she also complained that I took a day off for my Dad's funeral, selfishly) so I told her to go elsewhere.
Another client who was having problems with her fella accused me of having a fling with him after I cut his hair. She was as mad as a box of frogs and quite honestly I don't get a thrill from cutting a mans hair.
A few clients have tried to bully me into doing colours on their hair that I know will not work. I stand my ground and my reputation means more to me than a few hundred quid of revenue.
With unpleasant/aggresive/patronising/rude people I manage them and stand my ground. I have the advantage of knowing my trade inside out and have learnt over the years how to bend difficult people. The other stylists shudder at having to cover my clients. I think my clients are ok.I make them laugh at themselves, and conquer their difficulties with hairdressers.
People are usually tricky because they are unsure, defensive, scared or suffer low self esteem.If you can find the problem, and solve it for them, they become your devoted client forever.