Smashwords

One of Smashwords' advantages is that it can get you access to a wide range of markets, including those you would usually be unable to get your books into. For example, it is one of the few ways authors outside the US can get books listed in Barnes and Noble, and their tie-up with Kobo has become more important in the UK since Kobo now supply all WHSmiths ebooks.

To get access to premium distribution, the book needs to be well-formated (particularly in ePub format) and will be manually checked before submission. If it fails you get an error message. If it passes, you get access to a very wide distribution network. Smashwords' other big advantage is that it aggregates all the royalties from these channels, so you only have to make $10 in total across all channels to get a payout.

Not just used by self-publishers, Smashwords also has publishers with accounts on there. Publisher accounts are more complicated, as several author accounts may be held under the publisher's umbrella. Authors who already have their own account can assign books to their publisher, or publishers can manage the entire author account as a "ghost" or sub-account for less technically savvy authors.

The advantages are obvious for tax as only one EIN or ITIN is needed by users outside the US. Also, having all royalties in one place makes accounting a lot simpler for a company.