The reason why Zhejiang Xinshan Company can use the Shanshan trademark is mainly because they have registered the "Shanshan" trademark with the Trademark Office of the State Administration for Market Regulation of China and obtained a trademark registration certificate. This means that Xinshan Garment has the legal right to use the "Shanshan" trademark in China and can legally use and authorize the trademark. At the same time, the official website of Xinshan Clothing also clearly marked its licensing relationship with the Shanshan brand, and provided the display and sales of "Shanshan" brand products. This shows that there is a legal authorization relationship between Xinshan Clothing and Shanshan brand. Therefore, from a legal and practical perspective, Xinshan Clothing has the legal qualification to authorize the sale of Shanshan brand clothing.