Is a ticket and hotel broker obligated to inform his clients of the amount of profit he makes from their bookings, given that some of them ask and are answered, while others do not care as long as they are satisfied with the price?

The questioner does not sell tickets, but rather reserves them for her clients for a profit. In doing so, she is in the position of a hired agent or a paid representative, which is permissible in principle. It is stipulated that the wage must be known, based on the Prophet's (peace and blessings be upon him) saying: "Whoever hires an employee, let him inform him of his wage." Therefore, clients must be informed of the profit margin because it represents the wage for this service, even if some of them do not ask, so that they are aware of the price of the reservation and the amount of the wage.