I have only had one dealing on a gun auction, and it went fine.
As a seller, show lots of pictures and good description, it appears to me there are many auction sites, but these two are ones that i think have many guns for sale on them:
http://www.gunbroker.com/
http://www.auctionarms.com/
You "might" get more money and you might not, might be better to just try to sell here on the trader?
Many members have a C&R (FFL) and some have FFL, so this might be a good place to offer them first?
Ed