Dark Souls 2 – How to Reach Iron Keep Chests Without Dying? Guide to Accessing Iron Keep Chests Safely

There is an NPC named Gavlan that will purchase items and equipment from the player. He is the only NPC that serves this function.

He is initially found in

No-Man's Wharf

but moves once you've spoken to him. This means that at each location until the final one, you'll only be able to sell to him once.

The second location is:

Harvest Valley

The third and final location is:

Doors of Pharros

Source is the Collector's Edition Guidebook, pg 428.

In order to reverse the hollowing you need to use the Human Effigy (like you would use a lifegem), not burn it at a bonfire. This means you're able to use the item anywhere, and can save them for right before a difficult boss fight.

As of Patch 1.03, you'll regain a small portion of humanity for helping other players:

Players now receive a small portion of Humanity after successfully assisting in a Multiplayer session instead of regaining full Humanity.

Finally, there is a way to increase your maximum HP when Hollowed:

! The Binding Ring will ensure your maximum health can't go lower than 75% when hollowed. You find this ring in The Cathedral of Blue, right before entering the fog gate. It'll be in a chest to your left at the top of the drawbridge. If you are playing Scholar of the First Sin, then the earliest Binding Ring can be found in Heide's tower of flame right before the dragonrider boss fight, there is a Heide's Knight sitting in front of a chest, tackle him and you will receive the ring from opening the chest.