destruk, you're way overthinking it. The idea is that you use the Serial Number to identify the device during registration, but actually register it with some unique identifier that you generate, then store that in the registry on the Roku. When the box is factory reset, that unique identifier gets wiped, thus breaking the link.
As for subscriptions being transferred when a box is sold, that's the original owner's responsibility. As a general rule, you should always factory reset a device (Roku or other) before selling it to someone else.
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