What creates rare goods for the community overall is trades requesting rare goods (let's say, offering B and requesting A) that are not taken. Good A will be given to the trade poster and no one gas to give them, so Good A is created. On the other hand, an equal amount of Good B is destroyed as no one took it.
This being said, the maximum of such trades that can be placed is one per merchant per 6h. For this to be achieved, all trades should be either instantly taken or not taken at all. A taken trade doesn't create rare goods, so if a merchant comes back after 2h, that's 2h during which the merchant is not creating rare goods.
Thus, as much merchants as possible should be busy asking A and getting their trade not taken (if A is the rare good). Thus, to help the community what A-boosted players should do is not placing trades giving A and asking B, but the opposite : asking A and giving B. (Highly counterintuitive). And then giving the A good they get (both from production and merchants) to just placed merchants (ideally with another player online), basically giving their merchant capacity to the player they're trading with.
I can get behind a "take newest offers first" strategy, and that is consistent with what I have been saying.