All items are traded between players. If sell something, that means you fulfilled another player order.
In a gang-controlled settlement, shop can be upgraded only once (directly to level 5 when built).
Allows to place orders and offers with custom prices. When you place an order, you pay immediately but receive goods only when some player sells them. When you place an offer, offered goods are removed from your inventory, bottle caps are received when someone buys your goods.
A fee is collected from a player when order or offer is placed. It's displayed near Offer or Order button. An option to cancel order/offer is removed for orders and offers placed at 5% or lower fees (you'll be able to cancel the order/offer for only 5 minutes after it's placed).