How many Nights in a week is your hostel full to capacity?

Hi Everyone

It is - 40C outside my door so I am hiding in my office with you guys
I manage a small home hostel in the Yukon Territory Canada
The # 1 challenge facing myself and my staff is greeting someone at the door who just arrived with no reservation. Many times I have to tell them I am sorry but we are already full tonight. They almost always reply with.." But how can you be full it is off season ? " I gently inform them that I only have room for 12 guests / night so I don't have an off season. I just finished doing my year end and in 2011 this hostel was full 75 % of the time ie 3 nights outta 4. What is the industry standard? Does anyone know??

How can I convey to the masses that they got to plan ahead if they don't want to be left out in the cold.