It is based on IP address. I have entered a review on behalf of a family who gave me a written blurb to add to my website. I was able to add that with no problems but then the 2nd time I was unable to add and that's when I learnt that it was based on the IP address that was posting the review. You should however not get the message you are talking about. It is once the review is entered that it gets submitted and reviewed which is the time that the IP address is verified. I'd contact the website tech support to verify what's going on unless they have changed things but they shouldn't know the IP address of the person posting until you submit it.