[mborromeo]

Apple introduced an API to check if the device is jailbroken, but after 6 months removed it without any explanation.

However you can still make some check, like to check if the path /private/var/lib/apt/ exists or not. Since many package managers for cracked apps are apt-based, you should be able to get most of jailbroken devices.

Sadly (afaik), no way to understand if your app on a device has been cracked or purchased.