Some places have "extreme" reviews because guests have been very happy or very unhappy. Weeding out the extreme reviews will lead you to mediocre places.
There are far more sophisticated ways to spot bogus reviews, such as "does the review include specific information about the ________?" For some reason, the inclusion of the word "husband" is a "red-flag" for a bogus review.
TripAdvisor has developed some pretty sophisticated algorithms to detect bogus reviews. VRBO/HA is not as advanced, although all reviews are submitted to the owner for a possible response prior to publication. There is a lot of suspicion that the reason that VRBO/HA seems to allow bogus favorable reviews to slip through, is because they don't want to anger their paying customers.
Google <reputation management> for a lot of info about bogus reviews, but please do not suggest penalizing places that have a lot of good reviews because someone is doing a good job.