Sorry to burst this bubble but comparing insurance rates is only good as a very rough guide. As per Mannings statement but also it varies greatly on when you get a quote form the insurers and also where you live as some suburbs have a bad insurance rating while others are better. Same car, same driver, different locations can drastically increase the cost of insurance.
Another example is sometimes a cheaper model might be more expensive to insure than the top of the range more expensive model due to less people claiming insurance on the top end model.
There are so many factors that it's simply too hard to say that this person is getting this rate, why cant I.
Best thing is to get as many quotes as you can with the same conditions such as excess, agreed value or market, see if they cover off gazetted road conditions and then seeing which is the cheapest then going back to all the others again and asking if they can beat it. A lot of leg work but can literally save you hundreds. It's worth the time.