There are so much rules, yet for some reasons apps that are free to download but require a subscription at $30/month to do any action (so, not even a freemium model and arguably qualifiable of scam) are present in the store...

Edit for the downvoters: I'm speaking of apps doing local data manipulation (in my case, I tried few photo collage apps), not something linked to a web service. Those should be one time purchase, not subscription based.