I think you can trust Goodreads's ratings when there are 15000 ratings and the average is 4.5. You can be pretty sure that's a good book. Compared to 4.8 rating out of 50 ratings.
Same thing with amazon. If there's 1500 reviews and 4 stars, you can believe them. But if there's 5 reviews and 5 stars, there's a big chance that author has sockpuppet accounts or his mommy and her friends wrote nice things about his book
