Google Play trending apps

I'm new to Android Apps and I'm interested to know how Google Play rank apps.

1. I found "Trending" apps in my country have only 500 download. So I found some online service that offer 500 download for 50$ (they offer country targeting). Is it really that simple to get your app Trending?

2. If I launch free beta app and pay 50$ for 500 downloads, and get app Trending, can I change app so other users need to pay for download?

3. Does "Trending" category on Google Play works only for…

Google Play trending apps