""Government representatives (and no one else, mind you) are given full powers to negotiate on their country's behalf, and at the end what is decided has full power over the countries represented — more or less.""
Which, for all the arcana, is a hell of a sight better than sending them home and allowing politicians and other civil servants to get their muddy hands on (and argue, cavil and debate on) anything. Nothing would ever be agreed upon if that happened.
Sit 'em down, lock 'em in, hold 'em to the agreements. Great, more of that please!