But doesn't Apple explicitly disavow secondary sales?
No way would they unlock a device like this for your relative. It's odd that they won't unlock it even for the original owner. In what cases do they even plan to unlock these devices?
They can't prevent it, but they can certainly disavow it. By explicitly saying they don't support it or by making it harder to sell to the next person like region-locked or console-locked media.
I guess I'm surprised they don't! As the other commenter points out they have a page dedicated to this. I conflated their stance on secondary sales with their hardware and software self-service hostility.
No way would they unlock a device like this for your relative. It's odd that they won't unlock it even for the original owner. In what cases do they even plan to unlock these devices?