In the book trade, a BLURB is the very short matter printed on the jacket or back of the book and elsewhere in promotional material. The term was invented by Gelett Burgess before the first World War. One can take a phrase or brief section out of a review and create a BLURB. This is perfectly acceptable practice. When someone agrees to give advance praise (or not so praising) and/or a review of a work, it's with the understanding that the publisher and author can glean BLURBS for promotional purposes.
How to get BLURBS for your work? Ask those you know with credentials. You could ask famous authors but they will most likely ignore you or send a form email telling you to contact their agent, who will then ignore you. Most of us know a few people whose credentials will look good on a BLURB, and who would be willing to read an ARC of our book. Think of local media people in your community, newspaper blurbs always look good. Think of your college professors, if their expertise would apply to your book. Think of other published authors. None of these people need to be famous, they simply need appropriate credentials.
And don't forget-- you can cut and paste. Like if someone writes back and says, "This completely confused me, I couldn't get past the first chapter, and your punctuation was atrocious. But I loved the dialogue." Then guess what you use, and forget the rest? "Loved the dialogue." ~ Really Helpful Blurb-giver and Author of 3 Novels.
(This post has been inspired by and in some instances, directly quoted from A Handbook to Literature, 8th Edition, by William Harmon and C. Hugh Holman)