I think I would agree that booting him off is the right thing to do at this time.
The person seems moe intent on baiting and antagonizing the situation more than actually finding a solution.
Sara has been patient, but I would not allow him to continue to post in such a disrespectful manner.
If he has a legitimate complaint, fine, but state it in a mature fashion.
If they can't, discussion's over.
That's been my approach with many of our rude clients and it seems to allow them to back down and discuss their concerns in a more rational way.
I just don't think this is going to be resolved the way it's going now, and I'm concerned that other new members will be put off by seeing this continued exchange.