You basically can't allow people to give negative feedback for a thing and have that feedback mean anything (ie affect recommendations for anyone but you or show it to other users) without insincere feedback being used to hurt the reviewee.
There are ways to counter this, the easiest is to not show negative reviews but count them positively, a dislike actually boosts them just like a positive review would. Not really recommended due to promoting rage bait but brigading would stop working.