The altruist has an effect on all map hexes that give you something (which includes the market for the subsidies option in place, the developer for the tools and the bakers for the sustenance phase). Therefore, if you go to a joiner and your altruist is on +3wood, with just 1 wood, you can get 2 planks (altruist gives you the other 3).
It means you CAN trade 5 wood for 8 clay: the altruist gives you the 3 missing wood items.
... at least this is the way I see it and play it.
I thought the altruist did NOT impact tools from the developer? Or am i thinking of something else? I had the impression the Altruist basically does not have access to discounting tools? Ill try to find where I read that from, i think it was in another forum.