I used to play a game called Nexus TK. Very fond of that game but it's way past its prime. The markets were good when it was in its prime. It did not have an AH and no trade chats or anything like it.
There was an actual Market Place. There was also an in game forum. While playing the game you could open the forums. There was a section for RP Events, Community Events, Player Events, Community Forum and Discussion, and lastly Market.
People could post what goods they have to sell. People could post what goods they were looking for. There was little Spam for selling in zone chats. People could go to the market place and show their wares in a way that nobody could steal them and they were in a market stall so their purpose was obvious.
I propose this.
Give us an in game forum. Separate it by topic and have trusted players moderate it so you don't have to pay for people to moderate it. There are MANY would would do this.
Give us a connected market place available for all levels. Naturally don't let the factions mingle.. They can mingle through the guild stores already.
This is my thoughts on how we could fix the zone spam.
Also make the market place near a park so we can hop on a carousel after a hard day of trade.
This is were my signature would be if I was allowed one.