Is it permissible to sell the bonus that the intermediary receives from websites, such that its value is deducted from the price of the commodity for the customer and she benefits from its value, or is this bonus the right of the customer?

The ruling here differs according to the questioner's situation: If she buys from the website for herself and sells to her customers, then she may take the website's bonus and sell it. If she is an agent for the website in marketing and the website gives her the bonus for herself, then there is no harm in selling it to others. However, if she is an agent for the customer in buying from the website, then the bonus belongs to the customer.