Can't trade for Embassy

Early in the game, you can trade an Embassy for 25gp. Later, after Commerce I think, you can't do this unless you have declared Friends (because you can only trade gp/turn with non-friends; you can't trade hard currency gp / loose change).

The bug is if you have an unbalanced Embassy with a civ (only one of you has the Embassy), you can't open the other Embassy to balance it because you can't trade gp; whereas if you have NO Embassy at all, you can trade Embassies just fine (because gp isn't involved, it's Embassy for Embassy).

These days, I can't trade embassies at any point in the game for 25 gold unless there is a DOF. The going rate is 1 gpt for an embassy, if they are neutral to friendly. When you sell your embassy for 1 gpt early on, the risk you run is that relations sour as the game goes on, and the price they want to charge for their embassy later in the game may rise to 2 gpt or more.

With BNW I'm still able to sell an Embassy for either 25gp or 1gpt after other civs discover Writing and before I do. After Currency (I think), the 25gp option goes away, which is the bug / breakdown in how it should logically work.

(Seems like I delay Writing more often than not, while AIs prioritize it, but that's kind of irrelevant to the point at hand other than it may increase the incidence of the issue for me. It's usually not an issue if you exchange Embassies 1-for-1, as thereafter in the game it's pretty much always on that basis. But if you have an unbalanced Embassy, and forget to go in and do the other half after you get Writing, then it's a problem. And note that the AI doesn't remind you... it is good at asking for a 1-for-1 Embassy trade but if you have an unbalanced Embassy the AI isn't smart enough to ask for the other half.)