Forget returning that much. Even just spending that much at Amazon to begin with should set off an alarms, e.g. is this a stolen card? money laundering?
Due to scale and efficiency, they simply operate via check list approach.
When I had an ecom company, a line worker used to check the package content and appearance (dents/scratches) and then he would measure it on a scale and check with the package's recorded weight before it was dispatched and algorithm would flag the orders where weight varied more than some specific ratio.
It was pretty rudimentary but worked at scale just fine.
Now, Amazon must also be using something like this.