I haven't done any serious iOS programming yet (might do in the summer), but if I ever anted to release an app, you know what's the first thing I'd do?
MAKE SURE APP RINGS HOME EVERY TIME IT OPENS TO SEE IF THERE IS
ANY URGENT MESSAGES I'D LIKE TO TELL ALL MY USERS.
I don't care the slightest if it's something Apple doesn't want you to do, or wants you to do over notification center, just do yourself a favor and create a direct channel between yourself and the customers (so that you can send them a message whenever you felt like).
If you had such channel, you could've told them (after an apology for the inconvenience it's caused) how to remove bills, and that you're working on the next version, and the buy button was a bug, and avoid 1-2 star reviews, and sell much much more (no one buys/download a 1.5 star app).
:) Well, there are rules, (official and unofficial) guidelines and "best practices". The first two, you can't break them, but you can break the third and still be in the App Store. I think an annoying direct channel falls in the third category. I've seen many apps/games do it. Two of them (of top of my head) are blockbusters and have sold tens of millions of copies combined: Doodle Jump & Jetpack Joyride. So, yes, you can do it and still be in the App Store.
Yes, we must be careful to use it sparingly and only in the extreme cases that could result in many negative reviews.
A real world example of how this can ruin your rating:
I use a text editor on OS X called 'Mellel'[1], which is available both in Mac App Store and as a direct purchase. It's excellent and supports RTL languages (Persian, in my case) better than any other text editor. There was a bug on OS X 10.7.4 that caused the cursor to disappear. It was a simple bug and the developers issued a notification to all non-App Store customers (they obviously have their emails) on how to remedy this issue, but it took them like 10 days to update the app on MAS, causing a few negative reviews.
If you had such channel, you could've told them (after an apology for the inconvenience it's caused) how to remove bills, and that you're working on the next version, and the buy button was a bug, and avoid 1-2 star reviews, and sell much much more (no one buys/download a 1.5 star app).