Buy and Sell forum?

I don't know, I think it would cause problems unless it was handled properly and there were big notices that the site takes absolutely no respondsibility for the legitmacy of items bought and sold on the site.

I think the telling words are in the first sentence here "for when you can't be bothered ebaying it"

Like or dislike Ebay it is a business and a big one at that. It costs money to use Ebay because it costs money to run Ebay.

MSE is Martin's business with few paid employees. Most of the Moderators are volunteers as can be read on their signatures. Would you expect them to moderator a board where people are buying, selling and trading for a profit?

Who would sort out the problem when an item isn't delivered or not what you expect? Or when something isn't paid for and the user disappears into the night?

There are forums out there which do offer such a service but it is tightly controlled because they are perhaps profit run unlike Martin's site which for many a month did not. Once Martin did begin to see a small profit this was kindly donated to charity and it is only in the last few months that paid employees have been taken on board.

Fraught with difficulties I am afraid.