Well, probably nothing...IF the Seller is knowledgeable about pricing, marketing, finance, negotiating, real estate law in general and real estate vocabulary in particular, navigating the closing process, qualifying buyers, and has a gut instinct about people. Seriously, what sellers see are the actions of an experienced agent making it seem effortless; what they don't see are the countless hours of education and preparation, and the endless phone calls from nosy neighbors and unqualified buyers that consume a lot of non-productive time. The benefits offered by having your property listed in MLS and available to show at any time is priceless. The benefits of having every agent in your community having detailed, accurate information on your property at their fingertips, provided in a concise format they are accustomed to viewing, is invaluable. There are a million reasons to engage a professional to represent you in a real estate transaction....not the least of which is the safety of you and your family by having prospects pre-qualified before interrupting your family life.
In addition to the above, there have been numerous surveys done which show that a licensed agent can sell your home for more than owners can generate themselves. CAN you do it yourself? Maybe. The real questions might be: SHOULD you do it yourself, and what is there to gain by trying?