You’re first readers are not some people you never meet buying your book from Amazon because of the reviews.
Your first readers are the early adopters, those willing to give you a chance because they know at least your digital persona.
Like the people from your writers’ group on Facebook or Goodreads. People with whom you communicate a lot before you publish. Most of them are non-confrontational people. They are people that prefer to keep quiet instead of saying something mean that will put you down. These people will give you feedback only if they have something good to say about you or your book.
If you are one that doesn’t understand that a writers’ group is about writing, and your opinions are full of hate and disrespect for others your book launch might be closer to failure than you think.
The writers have that talent of making words powerful. If they like you, they will be your first readers and if they like your book they will promote it to their readers.
If you are the hateful, incapable of understanding irony, troll of the group, they will just ignore you and your book altogether.