With modern code locking, I wonder whether any of these could end up being being bricks, in the same way many Apple devices become bricks when the previous owner fails to unlock/unlink them prior to sale.
Of course, they could always choose to upgrade the firmware later to brick its functionality, but most device manufacturers seem to be increasingly hostile to resale. Or is that perception only in my imagination?
Do your research on the particular item you want to buy first and make sure you ask the seller whatever quesiton you may have e.g about resetting the device or having any system password etc.