Then there's BookBub. Every day the service sends you to three or four links to fiction, which links allow you to order the books as e-books for between five dollars and nothing. You might suspect that these are no hope books but sometimes you have a book by Isabella Allende, for instance. Using the service you can get a lot of books for absolutely nothing.
What are the limitations of this service? There are certainly days when you can despair of the taste of the Anglophone reading public based on what is offered to you here. How many detective series does one world need? How many fantasies about people growing up with magical powers, which they used to tame dragons or save the kingdom? How many imitations of the Hunger Games? The service is obviously meant to suck you in to buy the next book in the detective series or maybe the previous ones, or other books by the same author who wrote that Dragon fantasy you liked so much.
Still, as advertising for books goes, it does offer you something. Whether does much for the authors so advertised I have to wonder.