I'm not a specialist in IAPs so maybe someone more knowlegeable can enlighten me.
As far as I can see, you can pretty easily have features unlocked via an in-app-purchase in Google Play. The IAP object allows to do that.
Then you can request the info on whether the particular product has been purchased or not.
However, what about quantitative purchases? Is it possible? For example, I want to have a couple of 'credit packs' in my app so that users can buy e.g. '10 credits' or '50 credits'. Sure, I could just add 10 to var_credits after a purchase but how would I verify that later? For example, the user could then hack the app's webstorage and manually add 1000 credits to their account and I couldn't cross-reference it with the 'has product' response from Google Play.