I just asked myself this question dealing with a client today. ARRRGGGHHH.
I once posted a thread about rude customers. (I had one contractor/client go for my jugular last spring because of a few things I didn't pick up on a floor plan after our firm went through a mutiny - 15 % of the staff walked out in 1 day - and a lot of us were scrambling to keep everything in check). I would have gone off on him but I kept cool thinking: braces to be paid for with cafeteria plan - check, vesting schedule for 401 K is higher in April - check...you get the idea. Today, I would tell him to 'eff off.
This is a different client I'm talking about now. Our projects with this client are winding down. She calls on the back end of the project looking for extra work for free - can you move this wall, can you help with evaluating this...(not billed). As I have moved on to other projects, I return her calls within 1 to 2 days instead up picking up the phone. Since she notices the difference from 6 months ago, she has gotten a little testy. In short, being the polite, polished and always at the client's beck and call routine was starting NOT to pay off, so I changed my m.o.
I believe in being nice...but firm. If you are nice and NOT firm, that's not a good spot to be. I don't think being an a-hole is the way to go, either. They can only get away with it for so long.
Post your opinions and stories if you like.