Or your cousin. Or your co-worker, Bob. A beta reader is someone who reads for a living. They differ from people who know you because, well, they don't know you. They don't feel as if they have to "be nice," nor do they feel tempted to be "snarky," and they certainly don't give you fake compliments or skim your manuscript.
I work with several beta readers who I have worked with for years. They are professional readers, who know exactly how to give you the specific feedback that you need and that you can make actionable. My beta readers provide you with other titles that are comparable to yours, they point out if there are any major bloopers, or questions that went unanswered. They tell you what worked - and what didn't. They use a particular feedback form and answer questions that are overarching but also specific. They love what they do, they are excellent at it, and they are very affordable.
Most of my clients use beta readers after we are done with the developmental edit, as a way of testing the material "in the real world." Because I work with several readers, I usually advise my clients to use three beta readers; one who is usually a fan of your type of manuscript, one who would not usually read your genre, and one who is more of an omnivorous reader. That way, we get the take of someone likely to enjoy your manuscript, someone less familiar with the genre, and someone in the middle of the road. You need to use three beta readers, you might want two. Or only one. But I find that using at least two will offer you a spectrum of feedback that is more helpful for you as you dive into a rewrite.
My background is as a story analyst - a kind of Hollywood beta reader, if you will, and so my beta readers have been trained by me to give you the same types of notes that is provided for scripts and manuscripts in the realm of entertainment. They provide two pages of notes and these are the questions that they will answer:
What was your overall reaction to the read?
What is the target market for this book?
List three books (published in the last five years) that you would compare this manuscript to, including author, publisher and publication date:
Please choose one (or more!), with remarks about your choice:
Is the premise of this manuscript:
A. Fresh and topically relevant in the current cultural moment?
B. Unique, original, ahead of the curve and provocative – in a good way?
C. A classic premise refreshingly told?
D. A bit too familiar or predictable?
Were the characters three-dimensional, believable and relatable?
Did the first chapter grab your attention and pique your interest?
Was the pacing of the narrative consistently engaging?
Was the conclusion of the story satisfying?
Was the “world” of the story described in satisfying detail? Why? Why not?
Did you have any questions while reading that weren't answered later on?
Were there any bloopers or major logic issues in the read?
What do you think the writer tried to achieve or express here? Was it effective?
Can you suggest a list of 3-5 “fixes” for the manuscript?
Whether you choose to get beta reads through me or someone else, make sure that the readers you will be working with are professional story analysts with a lot of experience. My readers are specifically trained and have worked as readers for years in some cases. They also have an overall mandate - identify what is not working and suggest solutions.