You are the seller and in the USA.
You shipped the rod to Erlanger KY?
If the rod arrived there safely, your responsibility ended right there.
Was the item damaged when you sent it?
Be helpful to your customer, but this is not your problem.
This is now between your customer and the GSP.
God help him.
He should open an Item Not As Described dispute with eBay.
Don't Panic!
He should state in the Dispute that the item was shipped via the GSP and was damaged in transit.
If necessary this should include phoning and asking to be referred to a GSP specialist.
This is you being helpful, as stated you are off the hook on this, provided the rod arrived safely in Erlanger KY.
Then once he is refunded by GSP/eBay/Pitney Bowes, he can re-order from you.
I would suggest however, for this second purchase, that you review your packaging* and that you look into using USPS First Class Parcel International, which includes Confirmation of Delivery.
This service is a little hidden on the USPS rates page, you have to continue scrolling to the right to see the rates. The Priority rates show up earlier but they are more expensive.
*The GSP is notorious for repacking items, and doing it badly. However, most damage in transit is due to poor packaging. Just try to make sure that your work is good.
