This is pretty cool, and I'm glad it uses Unity's IAP -- I got it hooked up on Google Play easily.
I don't know if you want to do support in this thread, but there is a problem if the app is deleted then reinstalled... in my game, if a product is bought, I hide its "Buy" button, and Google is supposed to restore purchases automatically if you reinstall, but there's no way (I can see) to tell that to the IAP Manager, so my Buy button stays active, and doesn't process again or go away.
Maybe I haven't thought about it much (I suppose I can call to one of the scripts or use some other action), but it would help if there were more examples to deal with that scenario.
Update: I tried to use "Init IAP Manager" as a listener, but there's still no good way to handle both Purchase Start and Purchase Process with the same Buy button, not to mention Google's auto-restore, or for that matter, the fail state if you back out of the purchase popup (basically, I can only get one or the other to work properly). I think this needs a proper listener.