The only thing about trading maps is that, in my experience, it takes so much to get them to a point to be willing to do it (I do play on MPE, in which the AI tends to be less cooperative with the human than in Classic). I rarely try to trade maps because I usually find I have to give a bunch of stuff away to do it, which makes it it a bad trade IMHO. If we are met by small explorer-type unit, we can certainly demand tribute. Even if it results in war, it is very unlikely there will be any actual fighting for several turns; time enough to either build an army or make peace. Trading techs is almost always useful, as long as we don't give away anything important or too useful for them. (I wouldn't give away Monarchy at this point). It would be nice to get Map Making if we can. If we are met or find a strong force, do what we can to avoid war without giving away too much.