I read your latest post: https://christopherbarrow.me/2016/08/11/reviews-heaven-or-hell/
You may already be going down this track, but we’ve been in touch with NHS Choices regarding some other issues recently, and although they often refuse to remove reviews, they do have a system whereby they can tell which IP address is leaving reviews, and if they do find that many reviews have been left from one IP they will clean them up.
The first step they will take is to contact the poster and ask if the review is legitimate, to which of course the poster would probably say yes. But if your client pushes for the IP check then they should be able to do this.
They are contactable at firstname.lastname@example.org but not on the phone. It’s difficult to get a personal response so I had much back and forth with them until I got escalated to someone called James who seems to be very helpful. It may be worth your client addressing an email to him (though he is still behind the same email address) to see if he can help out!