getting a 20 word blurb endorsement from a well known author that your publisher can incorporate into the front cover is the way to go.

That's what I did with NOT WITHOUT ANNA. The front cover has an endorsement from Katherine Sutcliffe.

On the hardcover inside flap is the story blurb and on the back is 5 more author endorsements.

On the paperback the back cover has 2 author endorsements and the story blurb.

they're worth their weight in gold when it comes to the 15 - 30 seconds you have when someone picks up your book and glances at it.