When you sell something, you can just add "Sold" inside the thread. Leave your price so its easy for people to reference when looking at selling their gun... the threads here are never deleted, they just won't be posted in anymore eventually. Eventually they will get locked.
"I'll see it when I believe it"
PSA: Please don't use photobucket to post images. When you go through one of the older picture threads and find a lot of dead photo links, it is because of photobucket. They limit the amount of bandwidth your free subscription pictures can use, and then make the photo unviewable. Please use imgur.com or another free image host that does not ruin picture threads.