It's not in-game
As I've mentioned in my review in progress for The Elder Scrolls Online, the game did not ship with an Auction House -- a system in place in nearly every MMO that allows players to conveniently buy and sell goods within the game. Apparently for developer ZeniMax, the plan for now is to use a third party system by way of an auction forum instead of an in-game solution.
Their reasoning for not including it in-game is as follows, "You don't necessarily want to do a global auction house for a game with one giant server because that generally leads to all the best gear being available at very, very cheap prices. A lot of times that can trivialize the game. You cannot have a healthy economy when there are no restrictions on getting the best stuff in the game."
That's odd, because it works for nearly every MMO out there, including EVE Online, which has one of the most thriving economies in the genre. Instead of just restricting items to certain player levels or making them bind on pickup, ZeniMax's solution is to encourage other restrictions such as "using an online forum?" Hopefully they find a better long-term solution for this outside of using guild shops.
Elder Scrolls Online [Twitter]