Gun stores will low ball big time, like one third of actual market value.
Selling on Gunbroker is easy and a nice Pre-lock S&W 686 will fetch a premium price with multiple bids. Plus there are seller protections and won't have to deal with the Craigslist types on Armslist.
Just make sure to take a lot of close, in focus quality photos from all angles with a honest description. If you have the original box show that as well. Do a 14 day auction and pay the extra for a featured listing so item comes up around the top of the search results, (makes a big difference).
Set a minimum bid that you'd be okay with but a good bit below market value and a Buy it Now price slightly above high market value (You can do a search for completed items to find recent sale prices).
Once there is a winning bidder they remit payment of your choice and provide their FFL info. I use USPS Priority Mail Flat rate box with signature required, never had a problem.