If Ebay have already refunded, then why would you need the item back?

If the customer is willing to post it back at their expense, then let them if you want it back.
But there is no need to actually return it, as they have been refunded.

@cjw99   As a private seller, you would be unlikely to sell another motherboard, at least in the near future.
and frankly, it is easy enough to pack and send something safely.

If your not certain, then you do a drop test.  An item should be packed well enough to be dropped from at least head height, without any issues.