Interesting, isn't it.
As a few guys suggest, there is a "Private / Shop" filter on the main Buy&Sell page if it really bugs you. If you're after some second hand gear, how cool is it to look through pretty much the definitive list of all second hand gear in Aus, all in one spot.
Speaking with some shops today, some shared that it's been great that they can readily take trade-ins now, knowing they can list them in the Buy & Sell .. which again, is a good thing for people buying new gear & 2nd hand gear.
though i found it annoying to see pages of new adds from one shop before reaching private sales.
Sometimes they do indeed clump together, and they are occassionally 'shuffled' to try and avoid this.
Regards the search - here's a time saver: Your search is remembered for you, so next time you want to look using the same criteria, you don't need to set it up again. Just look down the screen on the main Buy & Sell page and you'll see "My Recent Searches"