Why am I telling you this? Because as much as I love guns, I also know that many folks don't. Selling your gun via a place like that is a win-win situation - you walk away with cash (or a gift card), and someone else gets to purchase your gun legally. If you take your gun into one of those city and police sponsored events, not only are you given a flat amount - when your gun could be worth much more than the $100 or so gift card! - but that gun is melted down. Sure, if you hate guns, and it's your basic every day gun, you don't care - but there are folks out there that will pay in upwards of $3,000 or more for collectible guns. You might as well get the most money you can for that dust collector, right?
By the way, while I am usually all gun-ho (haha) for selling items via Craigslist, be aware that it is against their policy to sell (or barter, or place a want ad) for firearms of any type. If you don't have a Gander Mountain location near you, and still would like to dispose of any firearms, call your local pawn shop or any firearms dealer - while not all purchase firearms, many do.