My opinion and nothing more:
If I am a member of a Guild, I feel an obligation to help out, to the best of my ability, my fellow Guildmates. "We grow stronger together" kind of thought process.
So I'll page through the Guild Trades pages and see what I can pick up, if not every day at least several times each week. Yes, I do try to keep a "reserve" of roughly 1000 of each Good in each Age (though I fall short in the early ones) so, if someone needs something special (set of Goods for an Alcatraz maybe), I'm in a position to help.
I had more advanced players help me out as I made my way to where I am now. I'm in a position to return the favor.