I like the one-time-IAP model. You can either make some of your game (a few levels, a fraction of the overall length) free then charge for the rest. This gives

I like the one-time-IAP model. You can either make some of your game (a few levels, a fraction of the overall length) free then charge for the rest. This gives me a chance to play your game, and if I like it I'll pay. You could also add a one-time-IAP which subtly improves gameplay. Most do this as a "buy to remove ads" but the Piggy Bank in Crossy Road is a good example of a clever use of this model. When the Honest Android Games blog was going, it would cover games with fair one-time-IAP to unlock full games, so don't feel like you're selling out because you include one purchase. After all, this was the shareware model in the 90s and that was more than fair.