Requirement này là could have vì người dùng có quyền đổi trả sản phẩm, nhưng phải xét nhiều yếu tố như thời gian bảo hành, sản phẩm còn tốt không, và sản phẩm có lỗi không
This requirement is because the user could have had the right to return the product, but have to consider many factors such as time of warranty, the product is still good, and the product has no error
This requirement is because the user could have the right to return the product changed, but must consider several factors, including the warranty period, the product was good, and the not guilty