Don't Take it Personally
When dealing with difficult clients, remember that what they are dealing with is completely about them - and not about you. The kinds of problems or issues expressed by the client are entirely about them and their inner state; you just happen to be in the way of what they’re dealing with. Even though they may be directing specific aspects of their anger or unhappiness at you, it can (and most likely is) related to other things in their life.
Many clients are most likely having problems at home, with family or children, or in other parts of their life - causing them to (albeit unfairly) take it out on you. Even if they are pinpointing specific things about you, it's most likely that something else initially upset them. So remember: Never take anything personally. Don't assume things - otherwise you’ll degrade the relationship between you and your client, causing more problems to ensue.