[mothered]

No need to purchase the Item, box the company Instead.

That aside, your method will work.
Thanks for the guide.

Can you explain that a little more for someone that's new to the game?

If the company requests the serial, you provide the one from eBay.

When they ask to return the Item for a replacement/refund, you send the box without the Item. Pack the box with dry Ice that's consistent with the weight of the Item, make a tear and tape It. When the company receives the box, the dry Ice would've vaporized (hence empty box) and because of the tape, It gives the Impression as though the Item was stolen during transit.

You'll receive the refund/replacement thereafter.