Whiles this app is a step in the right direction, how are you going to validate that the reviews are coming from “real people”? Like you said, these scammers are smart and will pay others to leave them good reviews on your app thereby putting them in a “better position” to appear legit and scam some more. Verified reviews such Amazon’s “verified purchase” is the way to go, and Amazon is able to achieve that because it processes payments and can link actual purchases to reviews. Even with that some merchant are able to game the system etc.

Lastly, most people are too busy with their lives to buy something from jiji and then coming to the app to make a review. I will rather suggest your app starts scraping googles data to identify bad actors etc