We get difficult clients every so often.

The latest one was somebody asking for the installation of a particularly unstable component on a shared unix server.

He was told (7 times, on seperate occasions, by three seperate people) that we would not be installing it, but kept saying but <Company name> allows it.

Finally, when I spoke to him, I simply said "then go sign up with <Company name>."

There's a certain threshold with clients, and it they go over it by a long way, it's advisable to seperate from them - it can only be harmful to your business if it continues to be a relationship built on unsteady foundations.

Simon