ESO has no system for trading, except for guild stores.
Most people are using up most of their 5 guild slots for trading guilds, as this is pretty much the only way to sell your items in the game, or find things you're looking for.
I'm in 5 guilds and now i'm thinking it might not be enough.
I had the pleasure to be part of the long term beta and have made many friends along the way. As a result, i have been invited to multiple guilds and even started one of my own.