And can you do it only using the in-product purchase service from google play? Could you explain me a bit more about it? Thanks, Noga.
Do you mean without the plugin? I don't know how to do that and there's no point when the plugin work's without a problem.
When using the plugin there is an event "PhonegapIAP: Has product", which checks if the user has already made the purchase.
I haven't tried it yet, but next week I'll be implementing it to my game and I might give you better answer than. Check out this q&a if you're having a problem with it.