But when a book blog, one of the outlets authors use to get their work out to you, the readers, is found out to be pirating, it's discouraging. Heart-breaking. Maddening. The blogs you follow to find books are trusted in the care of review copies and tours, and when they breach this trust, it's easy to question what blogs can be trusted. And how do you know?
For that question, I'm not sure there is any way to be sure, without a shadows of a doubt, the blogs you read and authors trust are practicing "above board". But here are some good barometers to go by:
When the blog does a giveaway, do they refer you to the author to claim your book prize? Most of the time, the giveaways are being offered by the author, and not the blog. That means, when you win a book, you have to contact the author to claim the prize. If not, see the next question.
If not, are they giving you a Amazon Kindle ebook, or a pdf file? Blogs given away prizes seperate from the author should be giving away a Kindle ebook, or Nook, or Kobo, or some other purchasable, site. Authors do not give .pdf or other file types to be provided to blogs to be given away at the blogger's discretion.
If you have any doubts, contact the author and ask them. I guarantee you, they will appreciate you reaching out to them.