What are the Sources of revenue of a travel agency?

Commissions
Commissions are the source of travel agencies' income. They are paid commission by the principal suppliers on the sales of their products and services. Usually the commissions are fixed. However if the agency is providing more business volume than usual, the commission rate could be higher. This is called override. An agency could pass some of the commission to the customers by offering discounts. That is the reason customers sometimes complain that the ticket of a particular airline is available with an agency at lesser price than another travel agencies. Airlines take the help of travel agencies to fill their empty seats at the last minute. Agencies could provide tickets for these seats well below the usual price.