I always prefer to stick to the point without getting into small talk with customers. I've also noticed that if they veer off course, you can simply delay your response a bit to get the point across that you've got other, more important things to deal with. They can't complain about "slow response times" in such cases because it's not as if they've got a problem or service related question which you haven't responded to, is it?

Ya I agree. If you offer live support you need to provide just that.

I would advise you to deal with clients who are a bit pesky & sticky in a manner in which I have done in past just stick to basics and gave appropriate answers to their queries ,no moving around bushes you will see they will also respond in same manner......

another advise or suggestion is if your client are rude and start using the F or S word then you can simply say :
'Dear customer if you keep using those impolite words then i we will need to close this conversation, thank you'

First of all ask them how you can help them and try to find out their problem by questions.

I always would prefer to be polite and informative to make such a client understand. But, it is true fact that politeness doesn't work always...