While the classification of market wards into departments can help, it is still a far cry from what everyone wants. While SE is working on a search function, we don't have it yet and the jury is out on how effective it will be.
What can we do? Own the issue ourselves.
I encourage EVERYONE to use the bazaar manager feature on yg.com. It's easy to setup. What you need to do as a seller is keep things up to date - name of retainer, what you're selling, the ward, online or offline. Then as a buyer, just go to yg.com and check the item you are looking for and go buy from the person listing the goods in the correct area.
I've done this a couple of times. Even finding the retainer in the lagfest of the big wards was not a problem. In and out in 2 mins.
USE the system to advertise your wares. USE the system to shop. Problem fixed.