Hmmm, yes, know what you mean - have had to "fire" my share of abusive clients over the years. The lesson is always the same: make sure upfront that everyone's roles and responsibilities - especially the client's - are very well understood. Take the time to discuss the relationship with client, even when you think it's going well. If it's really not working, cut your losses sooner rather than later, but make sure of course that client has adequate notice and that you are not found wanting in terms of your own responsibilities ...