Just to see if the aliens are stupid?
I think I had offered Yor something like "Advanced Aquatic Colonization" for "Aquatic Colonization", which was refused despite the "close" realations.
I usually try some money during negotiations, to give me some idea of whether it is worth trying other combinations of trades or what sort of techs I can squeeze out of minor races. Sometimes they won't give something at any price (I click on my money, an amount comes up which is less than my treasury but still displayed in red), sometimes I am only a few bc's-worth away from a deal.
