Hoverboards were a big one a couple years ago - burned a few houses down and killed at least one kid. The vast majority of brands of hoverboards sold on Amazon, as far as I know, were private labels from the same handful of Chinese factories.

I would also especially worry about cosmetics and baby products/toys and I hope nobody's buying power tools from Amazon. There was an article here on hacker news a couple weeks ago that mentioned a lady who was (partially?) blinded by an unsafe dog leash she bought on Amazon.