While you may be able to distribute your book on Amazon directly, thus avoiding our 10% commission, you won't always get more money by doing so.
KDP (Kindle Direct Publishing) says you can earn up to 70% revenues from your books sales. Yes, but only under certain conditions!
As you can read on their list price requirements, you'll only get a 70% cut if your book is priced between 2.99 and 9.99 USD (side note: $1.99 appears to be the best compromise between revenues and number of copies sold for fiction books).
And even though you may fall into this price range, Amazon will add a "delivery cost", even for eBooks.
If your book does fall into the 70% category, even for Digital books, you must pay a delivery fee per MB when publishing with KDP. For instance, for every sale made in the US, you’ll have $0.15/MB subtracted from your royalties.
You may feel you should still go direct, so you can put your book on KDP select, but be aware that this means giving them exclusivity rights for an automatically renewable 90-day period. This means you cannot sell your book via any other platform or channel during this time.
However, if you publish through StreetLib instead, you can earn more royalties, have a constant distribution fee that does not depend on file size, enjoy no exclusivity and, to top it all off, reach a whole bunch of other bookstores.
Oh, and by the way, check out this table of royalties to see what you will earn from the Kindle Store via Amazon KDP or StreetLib, depending on the book price. Enter your file size and the rest will be calculated automatically. The table below is one example with a 5MB eBook for USA users.