After sales service

My son bought a mouse. After he open the box the mouse was to small for his hand. He took the mouse back the next day. There was nothing wrong with the mouse. The sales person did not want to take it back because my son opened the box. He was prepared to buy a new box and lose some money but the sales person did not want to reason or understand the situation. My son did not buy the box he bought the content and according to my knowledge we have 7 days to return a item. We will not go back to that company.