A very interesting question. I'm trading in a Note 10+ trough Samsung. This is the trade in email I received from them pertaining to the trade in condition.
Does the device turn on?
The device must start up to the home screen and function normally
Will you factory reset your device before you ship it?
You must factory reset to remove all personal data from your device.
Is your device free of cracks?
The screen and camera lenses, if applicable, must be free of cracks and function normally.
Ensure the device is not blacklisted.
They do want the associated google account removed watching their preparing phone for return but I see no mention of the S-pen. I would hate to lose my $550 trade in deal over a S-pen though.