Is it permissible in Islamic law to add a percentage to the price of an airline ticket before purchasing it without informing the customer, in exchange for the office's fees, money transfer, and fluctuating exchange rates?

There is no objection to selling airline tickets to others, if the seller owns the tickets before selling them. The sale here is valid through "bargaining," meaning agreeing on a price without informing the buyer of the capital cost.

If the tickets are not owned by the seller at the time of sale, they can be sold in three ways: 1. Pre-purchase the ticket and then sell it to the customer through bargaining. 2. Promise the customer to buy the ticket and then sell it to them on a "murabaha" basis after acquiring it, informing them of the original price and the profit margin. 3. The seller acts as an agent for the customer in purchasing the ticket for a specific commission, and any discount goes back to the customer because they are the buyer.