That's not really the point is it Observer. Whether it's Guilds people or Careers people, they organised the event between them so should also have organised for the room to be cleared up properly. The point is that someone who was connected with the fair should have cleared up after, not Event Monkey who, I assume, was using the same room in the evening for a different event.
Speaking as soneone who often has to use rooms other people have used earlier in the day, it's not fun clearing up other people's mess. For instance I'm on the choir comitee and last Thursday the Hall hadn't been cleared after the external event that had been on in the Hall during the day so we spent the time we'd intended to use for other things clearing the hall so it was in a usuable state. In this case it was a Conferences problem as the event on during the day had been external but the same applies to everyone who books a room in college.