What is the main problem on Amazon? Is it fake reviews? The glut of cheap knock-offs? Or Amazon itself manufacturing popular items thereby using the store as a

What is the main problem on Amazon? Is it fake reviews? The glut of cheap knock-offs? Or Amazon itself manufacturing popular items thereby using the store as a free channel for testing out what works? I am trying to understand fake reviews, is the issue competitors destroying their competition with fake reviews or products paying for reviews of their own products?