None of those things? That's odd, because with freemium apps on iOS, IAPs require passwords, just as apps do by default. You can't turn that off. You can, however, turn off in app purchases entirely in the settings.
Apple do use 'free' in the store listings, but only where the price normally goes. Seems reasonable and consistent, no? Just like just having 'install' where the price normally goes on the Play store.
Apple identify right under the name, at the top of the listing 'Offers in-app purchases' when the application does. They always have.