When you "spend" Google Play Credits in an app, Google Play treats those credits the same as if you paid with real money: they took 30% (their take isn't so steep today), I took 10%, and then I sent the user/buyer the remaining 60% directly from my bank account (I used Dwolla back then).
It was risky because I didn't actually receive any money from Google until about a month later.
What you did was money laundering. And big chance for getting in trouble if let’s say ton of credits come from fraud/stolen and then google pays out to you and then crawl back once they realize is fraud.
I’m curious how you didn’t get into money laundering problems.