Yes, it's true. There are paid reviews on Amazon and Goodreads.
Some of those reviewers have been identified. In the cases where sufficient evidence has been presented and Goodreads staff has chosen to act upon that evidence, reviews have been removed and accounts terminated.
As far as can be determined, no reviews or accounts have been removed from Amazon, even though Amazon has similar prohibitions on "commercial" reviews.
How many reviews are we talking about?
Let's get some numbers from Amazon profiles just for the reviewers who have been removed from Goodreads.
Currently has 219 reviews on Amazon
Currently has 535 reviews on Amazon
Currently has 752 reviews on Amazon
That's right, folks. Three reviewers, 1500 reviews. Almost all of them are 5-star ratings.