Are there no other publishing platforms that do this for a flat fee? Apart from taking payment and applying DRM, what else is involved? Checks to ensure the author is the legal owner of the copyright?
As far as I can tell, the check is basically a tick-box declaration that you have the rights to publish. Amazon also want tax and payment information.
Some self-publishers publish on Kobo, but they're a bit opaque on what their cut is.