I had a similar thought when I first heard about it, but then decided that I should give it a try as I am always dismissing things out of hands for believing that they are scams.
One year later I've quit my job (full stack developer), and sell full-time on Amazon and have never been happier. My current listings generate the majority of my income and require just a few hours a month to maintain.
For the rest of my time I do whatever I want.
It's not that things are inherently scammy, or unscammy. It's just things are or aren't easy based on your ability/work ethic, and the competition is or isn't steep based on how uninspired you are when competing.
The whole "cheap chinese knockoffs" thing is dismissive and frequently inaccurate. The great majority of things that people purchase from Walmart/Amazon/Target are manufactured in China, full stop. Some of it is cheap, yes, but no more or less than the ones by the "name brand" private labelers.