In "Sell Gear," you can sell the gear from your inventory.
You can even sell all gear of the same grade all at once.
However, you cannot sell Resonance Gear or gear with Spirit Attire stats.
If you sell gear that has been enhanced to level 1 or higher, you can recover the Zeni and enhancement items that were used to enhance it.
Gear of a higher grade/rank will sell for more Zeni.