About BookBub advertising
From the site:
BookBub is a daily email that features limited-time discounts on ebooks. More than 1 million people with tablets and ereaders have signed up for BookBub to learn about price promotions on acclaimed ebooks that match their interests.
Publishers and authors pay us to promote their limited-time ebook discounts to our audience. We can advertise promotions running at any retailer including Amazon’s Kindle Store, Barnes & Noble’s Nook store, Apple’s iBookstore, Google Play, Kobo, Smashwords, and others.
Like other daily emails, BookBub is an “advertorial” newsletter. This means that although our email consists of paid advertisement listings, we have an editorial team that approves only the listings they think are the best deals for our subscribers.