There has never been a better or worse time to be a writer. The evolution of self-publishing has created an opening for anyone to put there work out there. It could be the next Great American Masterpiece or it could be just another Piece of Garbage. The truth is the reader is not going to know. You can read the blurb, but is it really going to tell you whether you'll enjoy the book's contents? (NO)
The endorsement or promotional description will vary from book to book. If you've written the perfect novel you want to hook the reader with a good blurb, and you can give them a couple of paragraphs of the things that drive your story. If you have written the perfect short story you want the reader to take interest, but a long or excessive blurb could give away too much.
"Never judge a book by its cover." We have all heard that, and in some cases we might even apply that saying to our lives, but I assure you if you're selling books it matters a great deal. Imagine trying to sell anything without a picture. Ebay, Amazon, Craigslist, and any other site gives you something visual to see when deciding to buy. Your cover might not sell a copy of your book, but if you don't have a cover or have a bad one it most definitely won't sell a copy of your book.
My goal as an author has always been to be read, but if I didn't want to be a bestseller then all my stories would be free, which some are at Bookrix, but now that I've been read I want to be a mentioned among the bestselling horror authors. I'm not being arrogant, however if I'm a bestselling author it means the public is turning to me for their horror needs/addiction.