People would be willing to pay if iOS let you test apps before buying them.
It wouldn't suit all apps, but it would be nice to have the option as long as the developer can set the time (or number of games) period.
If I had the option, my current game would have a try before you buy option, but it would be quite short to match the game. Something like 3 games to make sure you have time to get used to the controls, but if you reach level 10, you know the controls well enough so that is your last free game.
The game I am working has several ways to play, but each game lasts longer. Perhaps 30 minutes in-game (therefore excluding menu and instructional time), but you get to finish a game if you are near the end.
I wouldn't need to tell the player how complex the decisions are to avoid the potential for confusion, but something that allows me to code when the trial ends would be preferential to a fixed time limit.