There's a very quick fix to protect against those free applications that have too many prompts to get you to upgrade or add on for a fee. Simply turn off "In App Purchases" in settings. The photos shown below are screen shots from my iPhone, I used the same method for my iPad, yours may vary slightly, but this should work.
Tap Settings, to find this screen. Scroll down a bit to General. Tap General.
Once in General, tap on Restrictions. As you see in the photo, my restrictions are set to OFF.
Scroll down and notice Restrictions > In-App Purchases. Button is set to On!
Scroll back to top, TAP Enable Restrictions. You may be prompted to create a restrictions passcode at this point. I was on my iPhone, but was not at my iPad. Just enter a 4 digit code you will easily remember.
Now simply go back down to the In-App Purchases button, turn it to OFF.
You're DONE! You may want to take a quick moment to see if you are protecting yourself in an application (a screen prompt should appear that says "You are not authorized to purchase from AppStore"). It has worked wonders for me and there's no more surprise on my bills anymore! You will have to disable the restrictions if you do choose to make a purchase within an application, just don't forget to turn it back on to stay protected.