What do you do when you get a customer that is a complete ass? I mean: yells at you, calls you a liar, etc. I know customer support requires you to repress your emotions to some extent, but that ends up just making you (at least me) feel worse.

Cancel his account? Take it like a (business)(wo)man? Both?

They can just run off and post in a forum like this that the customer support was terrible, when they, in fact, were terrible customers. But, of course, they aren't the ones who have to be concerned with their reputation.

As someone else posted, it is ok to fire your customer. I personally wouldn't tolerate that and to me, it isn't worth the aggrevation. If they post something, just reply that you weren't able to satisify their needs and that you felt they would be better serviced elsewhere (something along those lines, but resist bashing them, even if they bash you).

It is a nice way of saying, heaven help the next host who they sign up with! You look professional, and everyone understands the basic idea. In the end, by being more mature, you come out on top and people will respect you. People tend to be able to pick up who is being rational and who isn't.

in no way you should tolarte customer who do badmouthing with you or use abusing launguage in writen communication. You can warn then not to use abusing laungage and provide them with guideliness of your company and the way you provide support. i am sure he will understand if not you can always suggest him to find another host.