We always recommend that you back up and erase your personal data before shipping the device to us. However this is not always possible, maybe you do not want the extra hassle of completing this task and that's perfectly understandable.
We will leave the device data exactly how we find it and none of this will be erased or changed in any way. Should we need to complete a software flash we will only go ahead and do this once we have contacted you and obtained your full permission to do so.