We are aware that spam reviews have been left on a number of stories. Unfortunately, the spam prevention steps we have in place will stop bots, but won't stop real people from signing up just to leave spam reviews.
What we have done is enable the option that lets authors delete named reviews (you've always been able to delete anonymous reviews). However, if you do spot an account leaving spam reviews, please mail either Temaris or myself with a link to the account's bio (i.e. the one with their user number in the address bar). That way we can lock the account to prevent it from being used again and we can delete any other reviews that they've left.