Any legitimate travel agent has registered with IATA - the International Association of Travel Agents. With this registration, they are given a unique number that is linked to their business or agency. When booking travel, if this number is correctly indicated at the time of booking, the agent is typically rewarded with a commission on the travel of up to 10%.
In some cases, travel agents may be eligible for 'industry rates' which are offered to travel professionals that often result in a favorable review of the property and increase the liklihood of the travel agent to reccommend to their clients, friends and family.
It can never hurt to ask for a discount, especially if you are in the travel industry.