I got lucky when I rented from these folks the first time because I called to verify the actual pick-up spot. Here's the deal: Even though your rental agreement says that you are picking up/dropping off at Toronto Island/City Centre/Billy Bishop Airport, there are no Hertz cars or counters anywhere near Billy Bishop Airport. The actual service counter where you do the paperwork is in the Union Train Station across from the Royal York Hotel. You can get the free Porter shuttle to the hotel, or take a cab (about $10). BUT -- you are still a good distance away from where the cars are actually parked. They are in an office building parking garage about 4 blocks from the station. This is where you return the vehicles as well.
SO -- if you get a good price for the rental and are prepared for some hiking, the Hertz Union Station rental experience is about the same as any other rental experience, BUT - if you are expecting the convenience of picking up a car a Toronto City Centre airport, it ain't gonna happen.
PLUS -- if you are unfamiliar with Toronto and don't need to be right downtown on Front Street, spend the $10 cab fare to pick up a car at a rental counter outside of downtown gridlock.