Rather than having the ability to have user-owned stores like in the 1990s MMO Ultima Online or a unified auction house like many modern MMOs, TESO only allows those within the same guild to buy/sell/trade with other guildmates. It's prospectively strong because all of the workings are there for a great user-to-user experience in terms of trading/buying/selling goods and equipment it's just not set up for it to work that way.

While there are merchants both in towns and sometimes out in the wild, TESO has a prospectively strong player economy (especially now that a economy-breaking bug has been fixed).