They are paid reviewers/users dude. In order for them to get payment, they must make only positive reviews. After all, only possitive reviews will be considered and i think this platform s for built for it. They must make positive reviews and that is the problem they reviews are not trustworthy and credibility questionable.
As i understand, the users who give reviews and are applying as Helpers will be strictly checked and qualified by the Helper Board of Lina Reviews as stated in their white paper. And it is in their Second Option where the qualifications(pertaining to votes mentioned above) are indicated which I quote "Publish lots of quality reviews, which are widely accepted(like/agree). After reaching the specific level, the reviewer will be promoted to Helper.Note that depending on the size of the system that this threshold will also increase accordingly."
And since reviews of users and/or helpers are made in the blockchain, it can never be deleted.