Use Smashwords. It’s the only way.
I didn’t realize this. It’s very easy to self-publish on Barnes & Noble, so I have always done it myself, cutting out Smashwords, and keeping the entire royalty for any books I sell to myself.
However, Barnes & Noble won’t let you set a price of free using their publishing tool. I’d seen other books free and wondered how it was done. Here is the secret: you have to publish your book to Barnes & Noble via Smashwords. At Smashwords, you set the price to free.
So what happens if you’ve already used the Barnes & Noble tool to publish and then you use Smashwords to publish the same book to Barnes & Noble? You end up with two listings of the same book on Barnes & Noble. One has the price you set in the Barnes & Noble publshing tool (which can’t be free) and the other has the price you set at Smashwords (which can be free).
Here is what such a listing looks like on the Barnes & Noble store: