yeah, trade advisor is WAY too smart... I just keep changing things until I'm happy with the deal.
My current (and only, so far) game I was isolated on a smallish continent for a good part of the game - a minimum of 3 ocean squares in all directions... well, not exactly, there
was a very roundabout sea route I hadn't been able to check, but still, for the most part I didn't do much exploring. Trading to get other people's world maps was a nightmare. They KNEW I was in the dark, and they KNEW I'd pay an arm and a leg. That may be the AI cheating (I'm just not sure), but it was very good in my opinion. Since I've been able to see the map, my world map has actually brought in money now and again to other civ's who apparently still can't see the whole world.
As for techs, I always try to stay ahead in the tech race, so I usually make a KILLING selling techs. Once I got to the industrial age, I sold magnetism and theory of gravity to 5 civilizations and got around 350 gold per turn plus around 500 gold (lump sum) altogether. I had nationalism already, so these techs only helped the AI get closer to me, not be equal yet.
In a third good trade example, I control all the ivory in the world (apparently there are no elephants on ANY other continents

), and I can get great deals to trade it. The Indians give me silk plus 20 gold per turn for my ivory. Some civs offer semi-old techs, but I can usually get a resouce + gold per turn.
All in all, I'd say trade is dependent on how powerful you are and what you control. If you are strong enough and have enough to offer somebody else, you can really do well. If you're small and weak, don't be surprised to get a "we don't see it happening" response when you ask what the AI would need to give you their maps. Trust me, I got that many times in Persia's early days.