There are several reports online that the "eprint-studio" app was offering ebooks without authorization. No proof that they were pirating, but it does look like it.
EDIT: They have a Youtube promotional/tutorial video that does promise any ebook for free, including books by Stephen Hawking, Dan Brown, and in particular, states the Harry Potter books are available free. The narrator does specifically state that they carry any ebook available from Google Play, etc., and their books are free.
Definitely sounds like piracy, which might account for the site being shut down.
https://www.youtube.com/watch?v=fvaZF7BR0sQ
If the original poster is interested in free/low cost best sellers and the like, I'd recommend looking into book downloads offered by a legitimate library.