My 2 cents: Get rid of stars and then have each reviewer submit something positive about the product as well as something negative as nothing is ever perfect. Eventually people will figure out the reviewers writing "it works too good!" or "it has no problems!" as negatives are fake. Even if the bots manage to get around the automatic detection (i.e. IP + activity tracking) they'll still be submitting negatives which will hopefully balance out their positives and incline the user to examine each argument instead of being subconsciously manipulated by the 10/10s and 5 stars.