Did you ever wonder how some books show up with a bunch of reviews either before it's available, or soon after? How do all those people get the book, read it that fast, and then leave a review? And, while you're noticing this, a lot of those reviews are left on the same day, or within a few days of each other....What's going on? Seems fishy, doesn't it?
Nope, those reviews are all legit. Authors who are savvy marketers put together what is known as a Street Team or Advance Reader group.
These are folks who have usually signed up for the author's email list and/or have asked to be an Advance Reader. They get the book a couple weeks or a month before the release date - for free - with the understanding they will let the author know of any typos or mistakes. It is also understood they will leave a review. This cannot be an explicit agreement, but it's the right thing to do.
Advance Readers, or the Street Team, can also promote the book to people they think might like it, using social media or word of mouth. Some authors have to-die-for Street Teams that hold release parties, arrange author appearances, and advocate for the book to their local libraries.
If there is an author you love, especially if they are not already a Big Name, ask to be an Advance Reader or if they have a Street Team. Just be sure you are willing to fulfill your obligations - many authors watch their Advance Readers carefully and drop the ones who aren't helpful.
If you would like to be one of my Advance Readers, send me a message at firstname.lastname@example.org and I'll add you (as long as you're already on my email list). I usually have projects coming up that could use reader input.