應該是說收貨地址無效，因為房子是空的（vacant），沒人住

同意樓上說的，我猜是客戶最近剛搬家，但是沒去亞馬遜改收貨地址

謝謝哈！這件商品是包郵的，我運費政策寫的是“If there is a wrong / undeliverable / insufficient receiving address which you left on Amazon, resulting in the item returned to the seller, you are responsible for paying all costs for return shipping, the original cost of shipping will not be refunded, and a 20% restocking fee will be charged.”
所以我是不是可以不退買家付的運費，還可以再收他20%的restocking fee？

你可以不退運費，但是restocking fee就算了吧，畢竟快遞沒送達，買家連碰都沒碰過。記得跟他說一下

樓上說得對。Seller Help里有說到：
“If an item is returned to you marked as undeliverable, issue the buyer a refund even if you cannot reach them by e-mail. If the address on the package was exactly the same as the address on the order, you can deduct shipping costs.”