I think that anyone posting a rating should also be required to post a comment.  If no comment is posted, the rating is automatically deleted.  If the comment is gibberish, then a ShareCG Admin could be notified, and the rating and comment could be manually deleted.  Otherwise, the member who uploaded the content, could respond to the comment in the comment section of the web page.  If the comment is "Don't download, It's A Virus!", the member can reply that the file has been checked, and does not contain a virus.  At other web sites (like Download.Com), when I check the ratings, I also check the comments.  If the comment doesn't make sense, or doesn't apply to me (E.G. "Doesn't run on Mac!"), I ignore that rating.  This not only helps the member to fix any problems with their upload, it also helps visitors get a truer picture of the pros and cons of the download.

-David