Your listings show that you will use usps first class international for shipping overseas, including to China. The service that the buyer is referring to is ebay international standard delivery which uses a ESUS tracking number. It can be slightly slower than first class and I have seen some reliability issues with it but based on your post, it sounds as if the buyer just doesn't want to any tracking number associated with their order.
First class international has tracking to some countries but China isn't one of those countries so if you use the stated shipping method then your buyer won't have tracking on their package. The problem with that is that if they open an item not received claim, you will lose the claim as there is no delivery confirmation on first class to China. But since that was the shipping method that your listing mentions, that is the way you are supposed to ship. Sometimes when your listing states first class international, the label defaults to ebay international and as far as ebay is concerned, you are allowed to change to that service although as a buyer I would be a little peeved if you changed the service. However, you will probably be peeved if the buyer claims an item not received claim too. Have you already printed the label and does it have a ESUS tracking number?
