Good or bad, a paid review is worthless. So are Amazon reviews, for that matter. No one trusts them, and shouldn't.
How can you make such a blanket statement like that? Sure, if a novel has only five reviews and they are all 5-star with glowing reviews, it's a good chance the writer's friends or family did the dirty work.
But a novel with say, 50 or or more reviews has a good-sized pool from which to draw initial conclusions. There are so many books available now--thanks to digital self-pub--that simply reading the first few pages in the 'look Inside" option isn't feasible--you could be stuck for hours reading those pages. But limiting your search to books with 20 or 50 or however number of reviews will give you a pretty good overview of what people think about a certain novel before you read the "look inside" pages before making a purchase.
I'm not saying I need 50 5-star recommendations before I purchase a book--sometimes I am the lone wolf in disliking a book every one else loves or vice versa. But reading those reviews certainly help me limit my search for books, for better or worse. Unless you've personally polled Amazon buyers I don't see how you can arrive at the conclusion that no one pays attention to reviews. If they didn't matter, Amazon would've pulled that option long ago.
So, yeah, they do matter.