I like being able to sell technology to the AI's, but they're not very good at pricing weapon or defense systems that I offer them.  There are two problems I've seen:

1.  The AI will offer money for weapon and defense techs that are strictly worse than ones it already has -- they are lower in value, have no passive abilities, and don't open up any new research opportunities.

2.  The AI pays more for improved weapon or defense technologies if you trade them one at a time, instead of as a bundle.  (I'm not sure, but this may only happen when their treasury is too low to offer their full valuation price for the tech.)

Both of these exploits put the burden on me to remember what I've already traded the AI, so that I don't accidentally abuse them.  If I could make a suggestion, the AI's could avoid both these problems by modeling what the "value" is for any particular level of a weapon/defense system, and pricing tech trades based on the difference between their current level and your offered level.  

For example, assume that an AI already has Laser III technology.  If I offer them Laser I, it should be worthless.  (Ideally, there should be some UI indication that the AI will give me nothing for it, to save time -- it could be in red, or not in the list.)  If I offer them Laser IV, they should offer me the difference between their Laser IV and III valuations.  If I offer them Laser V, they should offer me the difference in their Laser V and Laser III valuations.  That way, I get the same amount of money no matter what order in which I make the trades.