If my unit stays empty do I still pay your fee?

Generally no, unless it forms part of a larger contract with several units (ie an apartment building). We try to fill vacancies quickly, but we do not charge fees during the intervening period. However, there are instances where landlords take this opportunity to do renovations or remedial works, etc. If we are called on to manage this work, pay contractors etc, we may charge a fee depending on the duration and scope of the work.