As a reviewer, this kind of spamming would be really annoying, and I can tell you that there have been all kinds of explosions of reviewers blacklisting spammy or unprofessional authors, so my immediate reaction to this is no, don't do it. What you'll likely end up buying yourself is an out with the reviewing community.
You have no guarantee that your reviews are all going to be positive, no author ever does, and if you look at the ratings of ANY book on Amazon that's been out for long enough, you'll see negative ratings. That's actually really good, as sometimes the things that bother one reader/reviewer can encourage another to pick it up. And, personally, if I see a book that ONLY has positive reviews, I tend to steer clear. It means the only people reviewing it are friends or family of the author, or that negative reviews are being suppressed. Neither of these are good things.
What doesn't look good, and is bound to make potential readers avoid your book, is a slew of negative reviews by people who haven't read the book but have decided they won't ever read it based on the actions of the author.
Some options for gaining reviews:
- Bookbub
Bookbub and similar programs get the word out to their subscribers about books that are on special or free.
Some of these services require payment by the author but do get your book into the hands of many readers. That said, it's usually on a list of 20+ books on any given day, and there's no guarantee these people will rush to read it rather than download it onto their kindle and not touch it for months if ever. BUT it does get it into the hands of more people, so your chances of them reading your work do go up.
- Giveaways
Whether in kindle orSmashwords freebie format, or through the goodreads community, there are a whole range of giveaways of typically between one and five copies of a book. Again, there is no guarantee of a review, but just having the book on a reader's shelf (which automatically happens when they enter, I believe) makes your book more visible to other readers, and usually the fact that they entered shows up on their goodreads timeline. LibraryThing also has a monthly giveaway list, but this is less well-known than the others.
- Goodreads Groups
There are all sorts of review groups on goodreads. Off the top of my head, Read it and Reap, Making Connections, and For Love of a Book all have some kind of semi-regular giveaway send outs. These are one of your better bets for ensuring a review, as these groups usually have a requirement of completion of a book (with an honest review) which counts towards the reviewer's points and makes it more likely they'll be approved for other books in the future.
- NetGalley/Edelweiss
These sites focus on reviewers, with electronic (and the occasional physical copy) available in exchange for review. This is one of your better bets as each reviewer has a percentage rating that goes down when they have books sent to them and no feedback given. I believe there's a fee for listing your title, though. Last time I checked it was about $150-$200, I'm guessing US, and I'm not sure if that's per title and if there's an account set up fee in addition.
- Contacting Users Directly
Have a look around on goodreads, twitter, Instagram and the like, see who's reading and liking books similar to yours, check out their profile and their review terms (if they have them). If they say don't contact them, DON'T CONTACT THEM. Most reviewers who write for other sites will have information about what they review and how to get in touch with them. Have a look at various blogs and review sites and find people you think will click with your work.
Make sure you're respectful if you do decide to contact them directly, don't rush them, don't demand things of them, make it clear that you're hoping for an honest review and would appreciate if they would consider you for review.
Though, before you do any of this, your job is to make sure the book is the best it can be so that when you are sending book, you're sending a quality product, because these people will be impartial to the work, and they will highlight those things in their review. Make sure you're not too repetitive in your writing, your dialogue and writing aren't wooden, and that your characters and story are fully formed. Get someone else to do a pass over for editing and proofreading (if you haven't already) because it's likely someone will keep track of any errors in the text.
Good luck!