What Danica said - at some point, it's going to become a funny story you can tell at parties. But in the meantime, just don't take it personally. 9 times out of 10, it's not about you - and a difficult client is only going to get worse if you take it personally.

I took an Improv course once. The type of acting where you just 'wing it' on stage with a group of other actors.
The first rule is never say no. When someone improvs its always 'yes, and..."
i think this is a good rule of thumb for difficult clients. Usually they need to know they are heard, that you understand, that you will strive to fix their problem. Most people will become less difficult if those things are communicated.

If they still are difficult then remember you don't know what they are dealing with thats causing them to act that way - but most certainly isn't you. So breathe and get through it!

That is such a good question. It can be really difficult. The mantra of "the customer is always right" can drive me crazy. I find that for me, I just have to take a step back and breathe in and out deeply.

I remind myself that my worth is not determined by what they say and then I make a funny story out of it.