While not a scam per se, ebook readers tend to be a big investment for the average hard working person. As an author/publisher, I want to give you some insight into the various platforms. As I tend to make the same royalties no matter where I sell my books, I am giving this to you as unbiased as possible for any person.
KINDLE: The kindle platform is awesome, Amazon has done an amazing job with their reader. It is super easy for an author such as myself to make their books format and display properly on kindle readers. This means you get the look and feel of quality with uniform results from one book to another. As for actual appearances of pages text and images, I have to say Kindle is in the top of it's league.
BARNES & NOBLE: The nook is a bit harder to format a publication for. Pages may not display as the author has intended, and quality varies greatly in the actual appearance of publications. Also, there appear to be fewer titles available on this platform. The devices seem to present publications with a little less quality than the Kindle.
KOBO: As far as I know they are mainly available in Canada. However, Kobo seems to have a smaller market share with fewer titles yet, and publishing titles on their platform is a pain for an author as everything has to be formatted specifically for the Kobo. This means re-typesetting the manuscript and uploading it. It would take quite some work to make sure the pages display as intended by the Author.
There may be other readers, or apps, but Kindle has the largest marketshare, the widest selection of titles, and in my opinion the highest quality of presentation. It just seems more professional all the way around. They even have software to let you view your digital publications youve bought on your laptop or any device running android, linux, or windows.
You deserve the chance to make an informed decision.