The Trade-net can be thought of as the common civilization of the Isles. Tradelands are part of the same economic system and can communicate, most commonly through Tradespeak. Even though individual islands might go to war with each other they will still be connected through the Trade-net.
Trade isles can be divided into three or four very rough catagories, depending on their distance to traderoutes and frequency of trade.
Major trunk islands
Tend to be large or central. Lie on major traderoutes. They have a high level of civilization (roman/medieval/renaissance).
Many ships arrive and leave every day.
Most buying and selling is done with coinage. Barter is usual only in bulk. (rewards most often in money. Items of interest are expensive and highly prized, or of moderate value and steady supply).
Close to main traderoutes. Have a decent level of civilization (iron age/medieval).
See ships arriving at least once a week, usually more, usually on their way to somewhere else. Coinage is used but barter is often acceptable (rewards will be small amounts of money, some items of interest)
Out of the way. Don’t have much to trade, and do so only a few times a year, normally sending the whole villages worth of goods on a flotilla to the nearest branch island. An unknown ship coming in to port is a noteworthy event. Civilization is usually of bronze age/iron age. Coinage is not used much (rewards will rarely be money or metal items – more usually soft tradegoods or ‘primitive’ magic). Most trade is barter.
May only trade once a year, or even every few years. Only nominally part of the Tradelands. Can be as low as stone age in level of civilization. Meeting voyagers from other lands is a major, lifetime event. Almost no coinage. Trade is barter and usually only for essentials or personal favours. (rewards are primitive services or exotic items of interest)