I applaud Zenimax for trying to develop something new and the GAH could be a good thing.
However all I can see right now is say each instance of your alliance has about 3000 players, that means if there are exactly 300 players per guild there will only be 10 or less guilds in your alliance area that really matter to the GAH. and any guilds that have say 50 members will have to shop on a GAH that is not as active as those top guilds with 300 members in each guild.
It seems to me that Zenimax is not thinking at all about the small guilds and how they will function in the GAH and I really do think its going to be an absolute mess for that type of guild to buy and sell things on a regular basis.
Now I know someone is going to quote me and say you can join 5 guilds and belong to one of the top guilds but I can guarantee that those top guilds will be full most of the time and therefore getting into them is going to mean waiting in line and paying for membership, guaranteed.
The GAH, from the way I understand it, is setting it up so there is elite status in ESO and that elite status is the top guilds that control most of the GAH market will be ruthless and unless you are in a leadership position in one of them it might even be very difficult to stay in their membership. If your buying and selling does not meet their standards next time you login you can pretty much guarantee you will be removed from that guild so they can sell a new membership to a new..."svcker"