Some of our products are refurbished by the manufacturer - these products are clearly marked as such in the listing or ad.
You can read more about what refurbished means here
The manufacturer removes the serial number as part of the refurbishment process to prevent duplicate serial numbers in their system. If you have any problems just drop us a mail - we'll support it directly.
All the manuals, firmware updates, drivers etc. are freely available on the manufacturer's website without needing to register the product with the manufacturer.