Virtual currencies are a scam on its own, but even games without them can be exploitative. The monetization of games has become so frequent, that's it's basically accepted as something ordinary. I've noticed that some developers don't even bother creating a currency anymore, you just get the Playstore € prompt for the item you want to buy.
Most free games are built on the premise that it's never-ending or always expanding. Either you can upgrade to infinity or keep playing, because they keep adding new content. I don't think I've ever stumbled upon a game where you have limited things to buy.
The only solution I see, which is just plain unrealistic, is to put IAP apps into a seperate category. I've started doing this, by not downloading apps that have the "Includes IAP" and I'm pretty satisfied. I don't think any game/app should be qualified as FREE, if half of it is locked behind a paywall.