建議先去開case，讓seller support處理，我覺得他們應該知道買家的稅號等信息

不用管他，畢竟所有財務方面的交易都是由亞馬遜處理的。但還是要發郵件跟他說：
“Please be advised that all financial transactions are handled by amazon. We don't process your payment but amazon does that for you. Please reach out to amazon and discuss your issue regarding tax and if you are tax exempt, only amazon system can add or exempt at the time of purchase. Again, we don't handle financial aspects of transaction but only ship items we they are ordered.”

亞馬遜是有提供“退還稅款”服務的。如果有免稅，買家需要出示相關的證明文件：
"Tax Exemption for Other Purchasers
All other purchasers using a tax exemption need to provide us with a copy of a state resale certificate, tax exemption certificate, or other acceptable proof of tax exemption for the state where the items will be shipped.
The documentation submitted should include the name of the seller who sold the items and the name of the organization that purchased the items."

這是“亞馬遜免稅計劃（ATEP）”：
https://www.amazon.com/gp/help ... 3D1-2
“Note:?
Even though you are registered in the Amazon Tax Exemption Program, sales tax may still be charged on items you order from any seller who lists products for sale via the Amazon.com website. Purchasers have the ability to opt out of tax exemption for a specific item in the single page checkout.”

樓主，這是買家跟亞馬遜之間的“交易”，跟你沒啥關系。如果他提交az，你肯定會贏的。所以不要退稅款