I think vexatious requests are so infrequent that I wouldn't want to invest too much time in handling those very extreme cases, because it comes along with a significant risk of governments invoking a claim that a very substantial application for information is vexatious.
In Ontario, we have what is called the continuing access clause. It allows people to order information on a scheduled basis. The idea is that you have an interest in some information, and you might want updates every six months. That could be perceived as being vexatious, when it's just saying, “I am interested in this particular topic, and I want to know what documents the government has every six, eight, or ten months.” I think there is an obligation for governments to work with those people to help clarify what they are looking for so that it becomes less adversarial. I would be very cautious about vexatious requests.