The two spaces work together but serve different purposes.
Listings and sales are for offering an item or a service, with a price, a category and photos. They appear in search and in categories.
The Community is for local exchange: giving something away, asking a question, reporting a lost cat, arranging a favour between neighbours, or sharing a piece of local news.
To avoid duplicates, Community posts don't mix into shopping results. If your goal is to sell, use Sell instead. If you want to give, ask or chat, the Community is the right place.