I've not really been digging-up much info about ESO until quite recently, so the following may be common knowledge to everyone here. I was quite surprised to discover this:
- There is no public global or local Auction House in ESO.
- Players who don't belong to a player guild can only trade directly with other players via a trade window OR via ingame mail (which apparently has a built-in Cash-on-Delivery (COD) mechanism).
- There are no player shops or vendors, so no way to advertise your wares other than spamming chat.
- A player guild that conquers a keep in PVP in Cyrodiil can open a public shop in that keep for as long as they control the keep. Any player in the game can buy from that shop, but only guild members can list items for sale.
- There are at least 18 keeps in each PVP campaign in Cyrodiil that can be "owned" by guilds, with each guild only allowed to claim ownership of ONE keep at a time (?). Players can visit multiple campaigns (by guesting), so there will potentially be many guild-run shops they can access.
- All player guilds have a "built-in" private shop which can be accessed by all members of the guild via the guild interface ingame, so guild members can sell items to each other.
- The maximum number of players allowed to join a guild in ESO is currently unknown (I have seen references to it being anywhere between 300 and "thousands"), but it appears that ZOS would favour large cap limits rather than smaller. Those members can be from any one of the 3 factions.
- You can be a member of up to 5 guilds simultaneously.
Now, the fact that there are only 6 ownable keeps in Cyrodiil may not be significant, seeing as there will be multiple PVP campaigns running simultaneously. Presumably at least 1 of your faction's guilds will own a keep (with a shop) in at least ONE campaign instance. Presumably players can port directly to the keeps owned by their faction (in any campaign instance ?) from anywhere in Tamriel ?
If you're not a member of a ANY player guild, your only way of trading with other players will be to meet them face-to-face and open a trade window, or to port to a keep in Cyrodill and browse the guild-owned shop.
Edit: Added some corrections and clarifications.