The ads in game are... Not only looking non professsional, but it is the way to render your game annoying, also people I know at least turn off their internet on their devices just to not have them, except if a special functionnality requires it (SAM in jetpack joyride is an exemple of that kind of functionnality). They are also, let's be honest, a money wh*re thing, people are not stupid, they know most developers do not choose the ads that will be displayed, that results in a belief like "they don t even care about the ads, they just want the money", even on a website ads aren't popular when they are justified, but in an application that you have downloaded, this is just wrong.
Up front payment is nice and legit, but fewer download:
-Not everyone is confident in paying for a game online
-Not everyone like to pay a non physical copy of the game
-the refund time on the playstore is ridiculous
-in some cases, the performance is actually a pretty big barrier "Will it work on my phone?"
-Will the game be worth it? (Popular belief: mobile games are short and not that great)
The last two ones being the most important for me, I actually bought a game on the playstore that was more than 1GB for approx. 20$, in that case it was worth it because I already knew it beforehand, the performances were the big question, it is actually fine on my device, but really even though I knew it wouod work, I was still worried.
In the case of C2, you have a pretty advantage: the user could test a demo on the web to know what to expect, heck if your game is free 100% you could even have the complete version on the web, and providing the app only for people that don't have a decent experience through their browsers.
The IAP one is actually pretty complex, it should be treated like dlc's, aka: If that is an important part of the game by itself, it should be already inside the game, if it is a skin or something, that is actually okay, also remember that a good player should be able to complete the game without needed to buy them, additionnal levels could be bought as packs of levels if there are a lot (but do not call your game free in that case, since some level aren't).
As for the completely free, no ads, no IAP games, the awnser is simple: just make your game popular enough to have a name, but I would think most people want to make money or even a living with games, if ads or abusive IAP are known as the only good ways to make money, then that would mostly tell that the market is not yet ready.