Discovered a weird thing today:
I published a game on Google Play and was testing in-app purchases yesterday with test account. Now every time I run this game on my phone, "On Purchase Success" event is triggered by itself! Even if I clear all cache and data, even if I uninstall and re-install the app, and even if I set my phone to Airplane mode. It's still triggered.
I don't use "Restore purchases" action anywhere.