Any kind of trade deal is one positive diplomatic modifier. Giving people free or cheap stuff doesn't necessarily make it better. When the AI isn't fond of you, it will offer you trade deals proportionate to your power/score/position ahead of theirs. When the AI is fond of you, they might offer decent price, even if you are more powerful. Even if they are orange face with you, if your ranking is relatively equal or behind, they might offer a substantial trade, if they are in a position of need, for their own lack of amenities or a strategic resource.