There are several authors that I enjoy that only self publish their books, so I purchase their books on Amazon and read them on my Kindle app.
I do take the reader ratings in consideration when buying Kindle books, but sometimes those ratings don't reflect the true quality of the book. Fortunately, Amazon has a liberal return policy for their Kindle books.
You have seven days to return a book for a full refund. Log into Amazon, go to My Account, Manage Your Kindle. A list of all of your purchased Kindle books will come up. Open the drop down list and choose the refund selection. Another drop down list will ask the reason you are requesting a refund. Confirm that you do want a refund and your credit card will be credited.
There is no reason to pay for a book that is of poor quality when purchasing an Amazon Kindle book. But be honest, don't request refunds on books you have enjoyed.