Never sold on there before, but I buy most of my guns off GunBroker. Really easy and trustworthy if they have feedback. You'll find the prices are a lot more palatable than local gun stores.
I'm 53 and have finally realized that I have more guns that I can really justify. I always saw some of them as investments so I've been thinking about listing some on gunbroker myself. It would be interesting to try listing a few here since then it could be FTF and save all the shipping and FFL hassle. Maybe I will try it.
I have had people emailing and wanting me to mail the gun just to them, but other than that using GB is really straight forward. Just make sure they make sure the receiving FFL will accept guns from private individuals and other than that it is rather easy.
When you are trying to figure out where to sell guns, ask yourself where you bought them? I have bought a dozen or so from GB. But I've actually bought more from the S&W Forums and the Ruger Forums (rugerforums.com). Both of them have very active Classified sections and you have knowledgeable people on highly specific firearms. Good people on both. I'm sure there are other maker specific forums where the same thing is true.