It’s sometimes tempting to think that the books might just be low-quality but otherwise legitimate junk – say, he’s running a vanity press that publishes anything to get the volume and doesn’t proof it much, so buyer beware. But in practice these scam ebooks are basically:
– Wikipedia articles
– chapters from other books with keywords find-replaced
– public domain stuff
– actual garbage generated by machines
– maybe some actual original material sourced from fanfiction type sites with the author giving permission. Or not.
The legit vanity press/self pub type places will certainly put out an ebook for you! They have the market covered and this guy is surely not part of it.