A new post to the Android Developers Blog details the measures Google is taking to address the issue of fake reviews or ratings on the Play Store. They are described as a combination of AI and human expertise. The post claims that they have already resulted in the removal of millions of reviews from the Store.
https://www.notebookcheck.net/Google-claims-to-be-able-to-remove-millions-of-fake-Play-Store-reviews-using-AI.383491.0.html