I arrived back in Europe yesterday and I gave Hertz a call regarding this verify status business.
Hertz were unable to locate any 'reservation on file'. I had to make a fresh reservation over the phone, which was a little more expensive than the AUD price. This was GBP.
The confirmation email arrived shortly afterwards. This quoted another price - much more expensive than what I was quoted over the phone. I called Hertz again. It seems that the difference in the two prices was the fee for a one way rental, which the agent hadn't mentioned during my original call. I cancelled the booking.
Back on to the internet and I finally managed to make a successful booking after three attempts.
Strangely, I did receive an email from Hertz during the week asking me to complete (I assume) my first unsuccessful booking. Unfortunately, the link in the email was broken, so I couldn't...
Palmer