What is the ruling on the additional amount taken by the distributor for using his private car or a rented car to distribute medical supplies, and is it obligatory to inform the employer or the buyer about it?

The agent is trustworthy regarding what he has been entrusted with. Therefore, it is not permissible for him to betray the trust and take an increase in price for himself without his principal's permission, based on the statement of Ibn Qudamah: "The agent does not possess the right to dispose except in what necessitates the permission of his principal." The agent can request permission from his principal to increase the price of the goods in return for his effort and expenses. If the principal permits him, there is no harm. However, without an agreement, it is not permissible for him to take anything except with the knowledge and permission of his principal, and the increase in price would then belong to the principal, not to the agent.