There has been news pieces about fake reviews that the owners of hotels have either purchased or generated by themselves. Then, there are complaints from hoteliers that people or competitors that have never visited the property have left negative/fake reviews.
I sometimes leave a short review of a hotel on TripAdvisor, as I often found TripAdvisor reviews of questionable quality. You can easily do the review using TripAdvisor’s mobile app i.e. while in a taxi.