Travel agents make in the neighborhood of $30k on average to start, although that figure only includes their salary, and does not take into account the possibility of commission (usually 15-20% on each booking, which can add up to potentially tens of thousands of dollars each year).
Most travel agencies are paid by receiving commissions from cruise lines, hotels, car rental agencies, or tour companies. Unfortunately, most airline companies no longer give travel agents a commission for booking tickets. If you are a self-employed agent, you are paid commissions. However, those working for a travel agency are typically paid an hourly wage. Some travel agents receive a percentage of the agency's commissions or a percentage of the amount of money they have brought in by the end of the month. Gives them a bit of an added incentive to convince a client that they don’t really want to take a weekend getaway to Montana; what they really want is a 14-day European cruise.
Numerous travel agencies make their money by charging customers a booking fee. If you can stay out of trouble while in Tijuana, this should be the only time you get booked. The booking fee is generally indicated in the final price of the trip for the customer.