From the rules:

"Space Trader is a bidding strategy game for 2 or 3 Players, in which a contest is held by selected member worlds of the Alliance. Players are given comparable cargo holds of Goods. Each world desires different types of Goods, such as weapons or chocolate, and will award Credits to the Player who offers them the highest quantity of the goods they want. After 3 rounds of trading, the Player with the most Credits wins."