I'd argue this is why you should distribute your app on the App Store, but don't rely on Apple to handle the payments. Make your app free, with a payment to your site directly, where you then provide an activation code or password, etc, to run the free iOS app. One additional perk is that you don't give Apple 30% when you do this.

For the App Store to approve your app, you provide a test username/password or authentication code in the notes to the reviewer. After the app is approved, you can then deactivate that test account.

This requires more development overhead from the developer, certainly. But the extra 30% you get in revenue and the comfort of being solely in control of your payment process can be worth it.

There are a few apps that do this, but not many.