28.3 Each trade must involve at least three trade cards on each side. A player with fewer than three trade cards may not trade. When negotiating a trade, each player must honestly inform the other of the number of trade cards he wishes to trade and at least two of the trade cards involved in the trade. This information must be correct - the remaining card or cards need not be specified and may consist of any commodity or tradable calamity card(s), regardless of what was said to the other player. A player may not show his trade cards to another player during negotiations, nor may a player inform other players of the details of a trade after it is completed.
EXAMPLE: A player, wishing to acquire grain, announces 'I want grain -I'll trade salt for grain.' He agrees with a prospective trading partner that he will trade three cards, including two salt, for a grain, an iron and two unknown cards. Ilia guarantees that the other player will receive two salt cards. An assurance that the third card is also a salt does not guarantee that the third card traded will not be a different commodity, or possibly a tradable calamity card. Similarly, our player can only be sure that he will receive one grain, one iron and two other cards. He has no way of knowing what the other cards will be until he receives them, although meaningless assurances can be given by his trading partner.