Q: Register Refurbished MacbookPro

This should have been done and you need to do it now:

What to do before selling or giving away your Mac - Apple Support

It erases the Mac

If you have problems come back with specifics of what problems and what model Mac you have.

You posted in the Mac Pro desktop forum but you say you have a MacBook.

Do you really have a MacBook Pro?  MacBooks and MacBook Pros are different

There is a 'fitness of merchantability' that should have eBay

accepting this as a return to the seller; it was not readied for

re-sale and you cannot use it as a computer. Maybe a brick.

Good luck with eBay & getting a refund...!