These were zones within the city where you had to travel between to find a player or their retainer shop.
The advantage to using the Market Wards was lower taxes, and also it was the only place a retainer can set up shop.
There were stalls where a player can also set up their retainer shop and decorate. The stalls became more valuable to the players when the ward would become overpopulated. Making it difficult to distinguish one retainer from another on the ward floor.
There can only be a limit of how many shops can be set up on a certain ward, and also later when searching was adding, you would only see what was being sold in that city, not the entire world.
As for the revisions to the Market Wards, going off by memory so excuse any mistakes here...
- For the first iteration, there were no distinction between any of the wards. Basically, imagine it was a giant flea market with tax deductions for everyone.
- Second iteration, they've changed the names of the wards in hopes that people sell similar items in the correct wards. Incentive was a slightly higher tax deduction of 2~3% difference. This was only partially effective, though people still sold everything in the first ward, which was Battlefield Gear at the time.
- Third iteration, they've added and made the first ward to a normal ward that had no special tax deductions.
- Forth iteration, they've added finally the ability to run a search query on the wards instead of having to explore each shop manually. This will place a marker on the shop that is selling what you want. You now as the buyer had the choice of going into the shop to buy the item, or pay an additional fee to buy it straight from the search query.
This Market Wards from 1.0 was essentially trashed and turned into what would be a global Market Board for 2.0. There are no longer any wards housing any retainers, nor are there any special tax reductions.