More results from support, google, com. Sometimes, a previous review is lost if the customer who wrote it has their personal Google account deactivated. If you see a review with a link and it hasn't been deleted yet, contact the customer and ask them to edit their review to remove the link before Google removes it. For a review not to be considered spam, it must comply with Google's review policy on prohibited and restricted content.
Most likely, there won't be any problems with the review itself. It's more than likely where the Google reviewer comes from. However, the person who wrote the review from the same IP address as other reviewers may not appear on Google.