Not sure what you mean by quality, You provide a cover and a book and set your price. They provide a place to sell it that everyone on the net knows exists and where they can get any other book under the sun. It's all free. The only thing you have to do is advertise. What more could you ask for? .
Amazon sells a Kindle reader. It's one of the most popular readers out there. You even sell on Amazon UK and DK.
I have 4 books out on Amazon and Smashwords. The advantage is that on Smashwords your book is distributed to Barns and Nobel, Kobo, Sony, Ipone, Diesel and more.
Yet I still sell more on Amazon.
eBooks are the future. With Amazon and Smashwords you get to keep all your rights. You get picked up by a traditional publisher you can still sell them the rights.
If you want your book to sell well all you need to do is market it. That's the only downside to self publishing these days/ . . . . .