Dealing With Disagreeable Clients

So it's been a while; it's been too long, in fact. I've been both distracted, busy, stressed, and inattentive in regards to my blog. I have, however, been having good conversation with both old and newly-acquired colleagues. Which leads me to my topic.

How do you deal with a client that is disagreeable?

I suppose it depends on a fundamental question: do you have a contract with them? If you don't, then you should. So I'll respond to the question for each situation.

Contract:
To be honest, this is quite simple. Remind them of the contract that you signed with them. If they're having difficulties understanding what's expected of them and what they should expect of you, tell them very plainly that they signed a contract that clearly states those things. If it doesn't, well, that's a different matter; it should, though.

You can be very cordial about things but still be firm. That's probably one of the keys to being a good professional freelancer. You're allowed to set boundaries for yourself, your clients, and your company in order to maintain an image of professionalism. And you can tell your clients about that, too. Just be sure to be tactful about it.

No Contract:
This is tougher. If you're working with someone entirely on the whim, it's hard to be able to tell your client that they're being difficult or unreasonable. However, the plus side is that you're not obligated to them in as legally-binding a way as having signed a contract with them would make you (granted, you don't want to just bail on them; that would be bad form). You can very politely remind them that you're doing this work without a contract and willing to coordinate with them as much as possible, but you do have the right to discontinue working with them if they aren't willing to cooperate with you. Plain and simple.