If you're using an Android device, you should be aware that some apps include in app purchases. You can disable this functionality to avoid random and unintentional chargers. Check out this FAQ to find out how to change your settings.
Android - How to disable in-app purchases
You can't disable in-app purchases on Android phones as it is the case for iOS devices, but still you can lock these features with a PIN (which will be required for each of your purchases).
Open the Google Play App.
Press your phone's Menu button and go to Settings.
Scroll to the "User Controls" section.
Tap on "Set or Change PIN option" and enter a 4 digit PIN.
Back to the "User Controls", simply check "Use PIN for purchases"
Note that: On the latest version of the Google Play app this option has been renamed as "Password - Use password to restrict purchases"
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