Alliance trading

i tried to buy some expensive wood off a member just now and it said "not enough people to complete trade" or something. What does it mean?

i think you mean not enough money?

was this the alliance marketplace or your personal marketplace

Maybe you don't have the population? I always thought you never needed people to buy something, only to sell but it seems that way from what you're saying here.
And alliance trading isn't in the game. You have to be selling in the marketplace
EDIT: buying and selling to each other in the alliance marketplace ^ isn't in the game