Apparently the XML files contain a lot of conditions for the various leaders to hate you, the player. Things like the amount of wonders you have in comparison to them, or your military strength compared to theirs, or whether you've ever won a battle, ever. Unfortunately, to the player this often just feels completely irrational and random. I was actually a proponent of the more 'masked' diplomacy, but I'd like there to be some kind of logic apparent in the other civs' behavior.
But yes, I've been able to successfully trade with various civs before, it just seems really sporadic. Early in the game it's easier, but in the late game I've apparently tripped enough of those random hidden switches with the AI civs that nobody really wants to listen anymore.