When I first saw this card I thought it was too situational to really be useful. Then I realized it can be a nice way to get King of Dale out on the first turn if you aren't running two Spirit heroes in your deck. All you need is a 1-cost attachment, something like Hauberk of Mail or Map of Rhovanion. I find that Dale decks can struggle on their first turn or so when they haven't had the chance to get their allies out yet, so anything that makes it easier to get your engine going as fast as possible is certainly welcome. Not to mention that thanks to Brand son of Bain you've also drawn two cards as well.

This card can be fantastic in a multi-sphere deck if you want to e.g. change the target for the Steward of Gondor mid game. If you played a lot of the cards from one sphere, but you lack resources to play cards from another sphere, pull Steward back to your hand with Bartering and play it on another hero.

You can also make use of it in a multiplayer game as a way of resource smoothing: if another resource-rich player plays an attachment on one of your characters, you can play Bartering, give him back the attachment and then play one of your own attachments at a discount.

If you own older sets, it also works BRILLIANTLY with Beregond - you can play a 2-cost attachment on him for free, use Bartering, play some other attachment on another hero at a discount and then play the initial 2-cost attachment on Beregond for free again. There, you just created 2 resources out of thin air.

It's a very useful card if you think about it. It may not be flashy at first sight, but I had great success with it. @ThimYorke has also featured one of its key uses in his review.