Collect Positive App Reviews
Negative reviews can have a significant impact on your app downloads. To keep a good rating, you can prevent your disappointed users from reviewing your app by placing a "firewall" that will segment your audience.
Start by asking your users if they are satisfied with you app. If so, you can ask them to rate it and redirect them to the store. If not, you can collect their feedback using a form, without bringing them to the store.
This way, you can understand why your users are disappointed without degrading your app's score.