Shipping/airfreighting personal stuff to Morocco (Casablanca)

I am being told by the relocation company that for us to bring our household possessions into Morocco - whether it be just a few boxes that are airfreighted or a whole container full, that to avoid paying duty, we will need something called a Change of Residence Certificate from the embassy of our country ( Australian). I've rung them and they are very puzzled about it. Has anyone else had to do this or had problems with being charged duty for household goods? So much of our stuff is old and I can't imagine paying duty on it!