how to reward the player after they install another game and how to check if they did install ? (Android)

I want to give the player the possibility to install another one of my games in exchange for receiving some rewards in the current game they were playing, i don’t know how to make sure they installed it and that they didn’t just visit the game’s page in the play store store. Any ideas ? Even making sure they gave a 5 stars rating is an acceptable solution.

@username

There is easy solution for checking that user installed your other app or not.
Simply check the bundle name of your app in the mobile if result returns true the give whatever you want.

private bool checkPackageAppIsPresent (string package)
	{
		AndroidJavaClass up = new AndroidJavaClass ("com.unity3d.player.UnityPlayer");
		AndroidJavaObject ca = up.GetStatic<AndroidJavaObject> ("currentActivity");
		AndroidJavaObject packageManager = ca.Call<AndroidJavaObject> ("getPackageManager");
		AndroidJavaObject appList = packageManager.Call<AndroidJavaObject> ("getInstalledPackages", 0);
		int num = appList.Call<int> ("size");
		for (int i = 0; i < num; i++) {
			AndroidJavaObject appInfo = appList.Call<AndroidJavaObject> ("get", i);
			string packageNew = appInfo.Get<string> ("packageName");

			if (packageNew.CompareTo (package) == 0) {
				return true;
			}
		}
		return false;
	}