To resell the hub, reset it (hub settings > show advanced settings > reset) so it's ready for activation by the new owner. When the reset is complete, shut down using the power button, i.e. press it firmly for a second and then give the hub time to shut down properly. If you have not had it online for a while, it might be trying to update its software, so don't just yank the power cord.
We can move the service over after the new owner activates the device if you send an intro email identifying them (or, alternatively, give them the order confirmation and they can show it to us).
Make sure the new owner is aware that there is no Camect warranty applicable to this hub, that the service is for the lifetime of that particular piece of hardware, and that it's the consumer ("Camect Go") level of service.
You'll have to agree on a price with whoever is buying. We have no recommendations in that regard.