The flea market

The flea market is the player-to-player market. It unlocks at level 15. Until then, buy from traders and keep anything a quest asks for.

• You can buy almost anything there, often cheaper than at traders, but it's never found in raid.
• Selling costs a listing fee, and you can only have a limited number of offers up at once; that limit grows with your flea reputation.
• Found in raid required to sell on the flea, according to the current data: no.
• Some items can't be sold on the flea at all. Traders buy most things, usually for less.

Before level 15, quests are the fastest way to get there: they give a lot of XP.