I've had an issue with tech trading lately that seems obviously bad/unbalanced to me. After searching through the forums, I can't find any mention of it. I'm a relative newbie, so I may be missing something obvious. Nevertheless:

Why would an AI early in the game keep on buying my techs, thus depleting his treasury and crippling his expansion? For example, I just finished a game as Drath in a large universe with difficulty set to Tough. The Terrans were right next door, and the Drengins and Yor were a bit further out. All were set to Intelligent. So I colony-grabbed like a madman and financed my expansion by selling every non-military, non-diplomacy tech I could to the Terrans. Some of the supposedly Intelligent Terran's choices were suspect to say the least. E.g., he was consistently willing to pay a decent price for tech four levels up the tree, and then still pay for the techs earlier in the tree. Why in the world would he do that?

More critically, why was he so spendthrift early in the game? At some point, why doesn't he realize that paying over his treasury to me is inevitably going to cripple his expansion and help mine? The end result was predictable. The Terrans decisively lost the race for colonies, and were then far, far behind in economy and technology. Their early tech buying guaranteed that they had no chance whatsoever.

In conclusion: Would any competent human player squander his treasure by buying up every tech offered to him during the expansion phase? If not, why would the AI do so? I've tested the problem in three games, and in all three I was able to cripple my neighbor and take advantage of his distress by grabbing the colonies that he would otherwise have claimed (financing the expansion with his money). I like the idea of tech trading in general, but I think that in reality it's the only really weak part of an otherwise admirable AI. I'm being led to the conclusion that I have to turn off tech trading unless I'm in the mood for an automatic route of the AI.