You can get insurance for nearly anything, but in this article we're going to concern ourselves mostly with earthquake and windstorm. Earthquake is the ground shaking disasters we're all aware of. Windstorm usually means hurricanes and typhoons, and other grades of tropical storm.
Now, most people ask: "Do I actually need earthquake or hurricane insurnance if do not live near an area historically prone to that?" The answer is, you might, and you should talk to an insurer about the risks. Nearly every part of the United States has some geological activity, and you might not be aware of the history. The largest earthquake in the USA, for example, was not in California, but New Madrid, Missouri. That earthquake was hundreds of times more powerful than the quake that leveled San Francisco in 1906, changing the course of the Mississippi, made it blow backwards for a time, shot giant columns of liquified earth into the air, and left disruptions around the area that can be seen by even amateur geologists to this day. Similarly, while hurricanes do tend towards the gulf, nearly every coastal part of the country can have them.
The good news is, the less likely you are to have a hurricane or earthquake in your area, the cheaper your premiums will be.
Insurers usually go with the premium their software recommends and they all use the same software. Earthquake and Windstorm insurance is managed these days by powerful computer modelling engines. These models have within them a powerful GIS database that encodes many of the factors about earthquakes and hurricanes that have been found by science. They consider things like soil type, how high off of the ground you are, and more. They analyze your property locations, how they are built, and how much you think they are worth, against the structure of the insurance you want and the kind of portfolio the insurers carries. They come up with an assessment of the risk to the insurer, and from that, they recommend your premium.
These models are very complex and quite capital intensive. For that reason, there are only a handful of vendors. The market leader is RMS, and they are used by nearly everyone. Nearly any insurer that uses some other software besides RMS is using them in addition to RMS, not in replacement to it.
Because you ultimately supply the input to these systems, you can control the raw insurance price insurers see for your properties. This raw number is called the pure premium. Commissions and other expenses bundled into your premium are placed on top of that number, but do not replace it. Modelling systems are smart enough to try and understand many factors about the structure of your properties but many insurers simply choose not to use them. Some of insurers simply don't trust the models at that level of detail. Others feel that over a sufficiently diverse portfolio, they tend to be risk neutral, so there's not much of a point to them, especially since many re-insurers don't even care about the structures of the buildings they are reinsuring, at all. If every insurer on the planet gets your quote with the same policy structure - such as deductibles and limits, and the same list of properties, they should wind up with the same raw number as the basis of the premium.
"Insurers use the same software, and get the same premium, but why is my bill different!" This is actually normal. Of course, there are differences in markups and commissions paid to agents, and more, but the biggest difference has to do with prudent risk management more than any capitalist conspiracy.
Insurance is about risk management. Insurers have entire books of policies for many people, and they need to balance that risk. Look at how many insurers went belly up because all they did was write hurricane insurance in Florida. Good insurers manage their risks by spreading them out across the world. To do that, they have bundled into your premium another number that represents a pricing signal they use to determine if they are writing too much insurance for one particular place and risk. This number is called the risk load.
The risk load is calculated very secretly by insurers, but it is always higher if they feel they are overbooked in a particular area and risk, and lower if they want to attract new business. It's the differences in this number that will drive premium differences. By finding an insurer with the lowest premium, you are looking for those insurers whose systems are telling their underwriters who wants you with the lowest possible financial risk to them. You are not only lowering your premium, but you are helping the insurance industry as a whole manage its risk.