Diplomacy-What do you think?

[Tamur]

You usually sell map info for 500? Try getting 5000, and you'll see that the Carthaginians offer is pretty mediocre. You can seriously pad your treasury exclusively by selling Map Info early in the game to your neighbours. Once you hit a faction who has significantly different map information than you, they will start paying much less, or trying to charge 7000 denarii for theirs.

Also, the Accept or... condition is because your map is valuable to them. It will help them plan attacks on your faction, since the computer factions use only the map info they have to make moves.

Re: the rest of the diplomacy system, part of it is simply patience. Check out this post in the Diplomacy thread in the Colloseum. It can take several turns to get a faction "warmed up" to the idea of an alliance, and alliances do last. I and many others have had alliances last 50 to 100+ years. It's a matter of building relationships with factions rather than simply marching in and demanding an alliance, then forgetting about them. Such an alliance is sure to break with the slightest provocation.