Matthias Staber wrote:
When exactly are pieces face down, when are they turned face up?
When using the "fog of war", you generally want all pieces face down except for villages and transport canoes forming a canoe line. Generally you should choose whether pieces are turned face up or down only during the movement phase, or when they are built.
This may seem a little fiddly, but it's useful if one of your rumor-pieces is masquerading as a transport canoe early on to deny an opponent passage through an atoll (or even an open-sea space) that somehow presents a bottleneck into "your" empire. This forces an opponent to build a war canoe to chase off the face-down unit before their explorations or transport can take place through that hex.
You also want there to be some doubt about whether those two pieces you just moved to that nice island tile within everyone's reach were a transport canoe and a colonist, or a war canoe and a warrior.
However, since I usually have canoe lines going through most regions of interest, I typically stack units face-up under transport canoes for personal ease of reference
Are pieces built facedown and do I have to trust that the other players are building according to the rules, like in block games?
Yes, there is a similar level of trust in CoP as in block games. You need to teach the rules well, so opponents can be confident they know what they're doing and why in the Build phase