In the United States, the typical commission charged by a real estate agent is 6 percent. As an example, if your house sells for $100,000 then you will pay $6,000 in commission, leaving you with $94,000 to pay off your existing mortgage and all the other fees.
Realtors use these fees for marketing, promotion, overhead, etc. Most of the time a real estate agents come in two forms: 1) agents that are good at getting listings then sit around waiting for a buyer, or 2) agents that have buyers lined up. These agents split the 6%, meaning each walks away with 3%. Selling a house is not difficult, and as the homeowner you end up doing a lot of the work anyway. For Sale By Owner or "FSBO" is becoming more and more common as people no longer fear the home buying and selling process.
There are a few professionals that you will want to use to make sure your transaction goes off without a hitch: a real estate lawyer, a title company, and an appraiser.
Back to our original example. The $6k that you would have given to your Realtor to help you sell your house. Can you think of other, more productive uses for that money? Down payment on a new house? Pay off your car or other loans? Killer vacation in the Bahamas to relax and plan your next move for total world domination?
A great site for learning more about FSBO is TheBestLocalPros.com, they have tons of articles on the topic and give way more in-depth coverage than I'm doing here. Real estate agents are a thing of the past. I really believe that.