You can do trials on the app store. It's just not the standard time limited trial that you're used to. With most apps, you can find a way to limit the app that is still within the rules. For example, anything that saves something you can just limit the number you can save. As long as you allow delete the app can still be useful as far as the rules go, but people don't want to delete their data.

I've had a lot of success adding free versions to paid apps and then upselling the premium versions while making some money with ads in the free version as well.