The key word here is trading. Barter does not involve the exchange of money so you shouldn't have any problems. Knowing who needs/wants what and who has surplus makes this work. Often the trading is multifaceted. If John caught a large fish but doesn't know how to cook and you know how to cook but lack onions you offer to cook the fish if can get to keep half or more. You swap a bowl of fish stew for a few onions. From someone else you get potatoes for the same deal.