I'll give you what I think are the top 5 answers to this question.
#5 - A Network
Your Realtor is a walking Rolodex of mortgage brokers, interior designers, architects, handymen/women, real estate attorneys, investors, inspectors, other Realtors, and most important to you buyers and even sellers that may be up/downgrading to a property like yours. Of course you can include more players, but you get how this network can benefit your bottom line.
#4 - DO NOT CALL
By placing your listing on FSBO sites and newspapers you are often just feeding a database that will be sold to - yep, you guessed it, to real estate brokers. So make sure you are on the National DNC list. This is a succesful lead source because about 80% of FSBO end up listing after they give it a shot on their own. That last stat is a NAR source.
#3 - Internet Advertising
Ok so the Internet has helped level the playing field to an extent. Here's where the edge goes to the Realtor again. Three Letters, IDX (Internet Data Exchange), mean that your listing does not reside in just one website. You get the most exposure by being part of this "syndication of listings" by having your home listed where the buyers are already looking. And of course there's also your local MLS.
#2 - Time (AKA Money)
From prequalifying your potential buyer appointments to doing Open Houses, (and board packages here in NYC,) and everything in between, an experienced Realtor will know how valuable your time is and will be considerate with it. While your Realtor focuses on selling your property, you can focus on whatever it is you do best.
#1 - Money in your Pocket
Have you heard how some buyers will automatically deduct 6% off a Fisbo listing before they even look at the property? This is just an example of the negotiation tactics to be aware of when dealing with potential buyers as a FSBO. If furniture is involved some will set a plateau and negotiate through the furniture.
The Real #1. Time on the market is less with agents because of all of the above. Making the decision to go with the right Realtor early on may help you save on mortgage payments and/or maintenance or home owner association fees.
Here in NYC we are seeing tons of lowball offers which add to the confusion of where real prices are right now. Good luck with your sale it is a wild market we're in.
[Call me if you're interested in speaking with the top agents in your area, I'll put you in contact with them - through my network. 646.442.7407]