Hey,
I absolutely don't agree about the trade tactics expressed in the article. First and foremost I think that even getting 1 Gold per Surplus Resource is better than having it piled up idle somewhere.
In the beginning when there's hardly any inflation 1-2 gold coins from each of a few opponents matter a lot. It gives you an edge.
+Relations
+Money (for Tech Race or similar)
+Causes others to depend on you.
+Could rule out other third party trade treaties.
-AI gets additional benefits.
+But we assume it's common that most players have standard military resources like iron. If you supply another player with iron he'll increase the total war costs (destruction) generated by him and his enemy.
You might argue that the other player will get an edge too. Yes he will compared to the other players (not you, as you're trading a surplus resource and getting money for it). BUT, if you do deals with multiple players your edge will be a lot bigger. In the end you could end up receiving 100 gold for maybe 6-7 resources. The nice thing is that these resources are spread out on multiple civilizations while you amass loads of money alone.
By using this technique I usually get more money from foreign countries than my own country would generate itself.
This is pretty much an implementation of neo-liberal economics. But as someone wrote above one has to learn to distinguish game and real life actions and morals.
Well, it really comes down to the situation in the game.
Say I'm building military because I plan to take on Rome in a few turns. Caesar has 2 GPT to offer me; the only surplus resource I can offer him is iron.
Does it really makes sense to trade iron to him in those circumstances? So he can build better units (Praetorians) that will, in turn, cost me far more in the long run? I'll lose more hammers through additional unit losses and encounter higher war weariness resulting in lost production, commerce, and research. All for, say, 20 gold (2 GPT over 10 turns minimum).
Another factor is wonders. Would you trade a surplus marble resource to another civ for a couple of GPT when you're trying to build the Great Library and they also possess knowledge of Literature? Clearly you run the risk of missing out on the wonder.
So, as is often the case in Civ, it depends.
That being said, if there's no other danger, I'll often trade a strategic resource to a distant civ that poses no danger to me. One of my favourite resources to trade away is any and all copper I have provided I have iron, especially in the long era in between the Colossus and the Statue of Liberty. The AI will pay through the nose for copper, even if it has iron. Though frankly, that sometimes feels like a bit of an exploit.
