Sadly, I have a poor opinion on paid reviews.
I sent off to one reviewer and I am certain from their response that they skim read a few pages only. Their comments showed that they hadn't read the story and had little understanding of the tale. They also made several glaring mistakes that showed they weren't familiar with the genre, fantasy. This is one of my biggest bugbears, that a paid reviewer may not like your genre, so how can they give a fair review?
One mistake the reviewer made was in quoting other fantasy authors and getting their names wrong. They mentioned Anne McCaffrey and her books, but misspelled her name and some of the books the reviewer mentioned weren't even hers.
The reviewer also commented on some of my fantasy creatures. For example krell, and said that is what whales eat. That, of course, would be krill. Now, having a name similar to a commonly used name...is that a big issue? If you look at English words and their spelling, there are many examples of how one letter can change the meaning of a word. For example, look at hell, hill, hull or pill, poll, pull, pall. All of these are completely unique words with unique meanings despite one vowel change.
Not all paid reviews will be problematic, of course and perhaps I just had a bad experience. However, I perceive the problem with paid reviews could be as follows:
1. The reviewer is being paid, so reviewing several books a day is worth their while. Say they charge a nominal £100 per book and they review say five books a day. That would be £500. By comparison, if they did the job they said they would, and spend 3 days reading one book, they would earn £100 only. So it is in a paid reviewers interest to review as many books as possible, as quickly as possible.
2. Is the reviewer interested in your genre? They may claim that they are, but how do you know?
3. It is far easier and probably safer to be negative about a book, especially for an unknown author. After all, how many publishers rejected J K Rowling? I bet they are kicking themselves, but the majority of unpublished books are likely to fail, so from a statistical point of view, giving a negative review is likely to be the best option.
All my reviews have been from customers. The vast majority are people I do not know. I have some exceeding good reviews from fantasy book review sites and these I treasure. I also have some bad reviews and these you have to accept. I have never asked friends or family for reviews. I trust the heartfelt reviews I have on blogs, Amazon and other sources far more than the one paid review (not Kirkus by the way) and sadly that experience really put me off.
I suggest self published authors think very hard about paying for reviews and that you question the person doing the review, to see if they are fair minded, and likely to read the book in its entirety.
If you want to look at my reviews to see what folk are saying, then check out http://davidburrows.org.uk/reviews.html
Best of luck in a complicated field: David