From my experience in Germany, it's 50/50. There are fake human reviews (Vine Club being a large part of it...), but there are also clearly auto-translated reviews (though they might be posted by humans). It's mostly on low-price items that are FBA'd or shipped directly from China.
yeah, real humans blast past captcha and enter real heart warming text about how great the product is but don't mention they are being paid to write this review and pretend the product is good. Let's tackle the real issue and like connect wires from the human to the computer and like lie detector style measure their blood pressure, heart rate, sweat, or...