Item possibly damaged in transit but well packed

[zeus1958uk]

Item fully tested and working before shipping but buyer claims that item is faulty and wants a return. This is why I hate sending items abroad but sadly omitted to strike the shipping overseas option. Can I take action against the courier including ebay's global shipping program? The item was very well packed with polystyrene but was obviously shaken so much during transit that it no longer worked when it got to the buyer. Or do I just have to accept it and never send anything abroad again?