Ah, thanks! I did search but obviously didn't dig too deep.
A buy and sell forum doesn't have to be complicated. Simply post a photo which includes the item for sale with a piece of paper that includes your screen name and the date. As with any other online classifieds, it is buyer beware. There really doesn't need to be any investment of time or energy into it other then creating a new section for this type of posting. If it were to take off and be really popular then maybe at that point in time some additional thoughts should go into expanding the experience. In the beginning it really is just a place to buy and sell items we all share a common interest in. Just like car forums etc.