I own the BCSE mod,
Customer Review Management for X-cart
One reason I like this -- it gives the admin complete control over posting of reviews. My store allows "anonymous" checkout, which means some customers are not "members" -- which means a legit customer may want to post a review -- so we have this mod in place and anyone can submit a review, and the admin is notified, then we approve reviews as they are submitted. I think this mod is a good solution and very reasonably priced for what it is.