Real estate agents must have a license from the State in which they work. In some States, a person who wants to be a real estate agent must go to a special school for a few months. They should be well organized and be able to remember people's names. They should deal honestly with people and have good manners.  Real estate agents have access to resources for assisting you in your home search not available elsewhere. When you are buying a home a real estate agent can provide you with objective information about each property, and give you advice based of experience. A real estate agent will help you  to make sure everything goes smoothly. I think word of mouth is the best way to find a good real estate agent. If a friend, colleague, relative, neighbour has dealt with one that gave good service, met the agent yourself and assess them. Select the agent that you feel is most professional and knowledgable in selling property in your area.

Useful book:The Consultative Real Estate Agent: Building Relationships That Create Loyal Clients, Get More Referrals, and Increase Your Sales