I haven't sold anything, but it depends on a number of factors, im guessing.
1.) The price of your apps on the store. Google takes 30%, but that still leaves you 70&. Say your game is $1, so you get 70cents per sale. That may not seem like a lot, but it can add up over time. Google and others have written guides about how to price apps, recommendations.
2.) Promoting. Promoting your game to family and friends may help, then asking them to pass the word along.
3.) Social media. Having a Facebook page and/or Twitter account can help drive traffic to your app on Google Play. More traffic > more sales. All of which increases the purchases.
Together, and depending on those factors, will determine if/when you get the $25 back.