As a mother I remember the necessity of burping the baby after feeding. You didn't always know what you were going to get. A nice quiet burp with no smell, or one that woke the dead immediately followed by a stream of vomit that smelled to the heavens. Book reviews are much the same. And they're just as necessary as that burp for the baby.
To me as a reader book reviews are not all that necessary. I choose books based on their cover, which makes me pick it up, the back blurb which catches my interest a little more and the first page. The first page needs to give me something I want to know.
Here in the real world of libraries, bookstores and readers groups that isn't always the case. Many of them want reviews and they want reviews from reputable reviewers like Kirkus and Pulisher's Weekly or the New York Times. On limited budgets this is how they choose many of the books they decide to purchase or represent.
As a new author many times, unless your publisher is huge, it's very difficult to get a review by Kirkus and/or Publisher's Weekly and my understanding is the New York Times only reviews the best sellers list. So how does a new author, especially a self-published author break the chain of no reviews? You research--and you keep trying. A recent article stated that a new author should send out 200 review copies to every place they could think of. For self-published authors this is a little stiff. So perhaps not 200, but as many as you can reasonably afford.
Should you pay for a review? Well, that's difficult to actually determine. It depends on the who is doing the review. Kirkus Discoveries accepts self-published authors. The price is rather stiff, but a good review there could really help you in the area of marketing your book.
So what if you get a bad review? Does that mean you should stop? No. In my humble opinion a bad review is just as good as a good review in many cases. It gets your name out there. Some people may not even read the actual review, just note that you were reviewed and therefore pick up your book and buy it, or ask their local library to order it so they can read it. Either way you made a sale.
So if you're working on a new baby, or have an old baby sitting around that needs burping, pat it on the back and find a reputable reviewer.