When you ship used items such as your own clothes to another country, this means that you are less likely to purchase new clothes in the country you have shipped to. This puts local businesses, and consequently the local economy, in a challenging position.
Customs authorities worldwide apply duties and taxes on shipments to protect their respective local economies, as well as to fund local services and infrastructure.
As this is a government mandated policy, Sherpr nor the courier have no influence on when and how these charges are applied.