How to unlock auction house tiers?

[Leem]

Hello,

What exactly is the way to unlock the different tiers in the auction house? Is it an eventual quest, something that is unlocked via accomplishing something, or is it a purchasable option at a vendor that I've missed?

Thank you.

[Tila]

The auction tiers are unlocked via quest. I believe on day 23, 48 and 68 if you follow the questline instantly.