Diplomat spy?

You can trade for 'Yea' or 'Nay' votes from the host nation your diplomat is stationed in.

Size up the number of votes a particular resolution will receive for and against it, determine which countries are represented by how many number of delegates, then proceed to barter with said nations for their vote favorable to your cause, possible only when a diplomat allows you to trade for votes.

Is there any way I can easily tell who has diplomats stationed in my civ? I've been clicking all the leaders one by one to see if I can trade votes, but would be nice to have a visual cue somewhere.

I could see what a real player, not an AI, was going to vote with a spy, how can the diplomat/spy possibly know that?

For Cultural Victory, Diplomate Spy is very good. It help you gain 25% tourism bonus, when the civ have different ideology.