[恕刪] 官網FAQ裡幾個相關的回答, 雖然沒有直接回答到期約交易的部份
Q: Trade - May I give away resources or buy services with them, for example,
to avoid being bothered by the robber?
A: No. On Catan, a trade always involves giving and taking resources.
Consequently, Catan’s trade law does not contain a “trade” of something
for nothing or for immaterial goods such as services.
==
Q: Trade - May I trade via a harbor where an opponent has a settlement?
A: No. You only have the possibility to trade with the owner of the harbor
himself, maybe by offering him something that he, in turn, could trade via
his harbor.
==
Q:Trade - May I trade “on credit,” that is, receive a resource now and pay
for it in a later round?
A: No.
==
http://www.catan.com/faqs/93?page=4