I have played actually quite a lot games using the technique of the "Emsworth Agreement." I was however always under the impression that it was allowed. Even more so when a poster asked about it specifically and linked to a thread that I posted in the Strategy & Tips (
(link) and was told that it is OK:
http://forums.civfanatics.com/showpost.php?p=4520705&postcount=392
As such I have been blithely using it whenever I got the chance to.
And not only that, I developed it and took it to a whole new level by having the deals being build up on each other, using large lump sums of gold, and using more than just one agreement. And exactly these 'improvements' are what makes up most of the insane results that you can achieve wrt you bank account.
If I may make a suggestion, what about simply drawing the line elsewhere instead of just dissallowing this technique. What I am thinking about is something like this:
The "Emsworth agreement" is by and large allowed with these exceptions:
You may not use lump sums to buy gpt, while techs and maps are OK.
You may not use gpt that comes from an earlier "Emsworth agreement"
Otherwise, it would be easier for me to simply give you a list of HoF games that are not to be excluded.