So, when ordering mail-order boots, the axiom is: Know thyself. Make sure you have an accurate read on your own foot. Call the maker and discuss your foot with them, your street shoe size, whether you think your foot is a little wide or narrow, that sort of thing. Then, once the boots are in hand, don't immediately slap them on and hike ten miles on a muddy trail. Wear them around the house for several days to see if they're going to be comfortable and fit well. If they're not right, and they're still clean, you can exchange them. That said, of course it's a bit of a crapshoot. Check out reviews of boots in Outside magazine or other outdoor-oriented publications, and glean something about the boot's fit characteristics.
Finally, this. Human feet fit a bell curve. Most people are average in size and volumemy size-nine feet are so common that shoemakers use this as their sample size. Other people have extremely large or extremely small feet, or feet that are very wide or narrow. I get mail all the time from people who wear a 15EEE and are bent out of shape because some mountain-boot maker doesn't craft a boot in their size. Get over it. Boot makers are businesses, not charity agencies. They can't make money making a boot size that fits some tiny fraction of the population.