Amazon's cavalier approach to verifying new sellers and their listings lets things like this get into their store.

They didn't care, but clearly their checks and verifications failed, so they were probably not fully aware.

It's their responsibility to know what is happening and to care what is happening on their store - just because they have completely vacated their responsibilities doesn't mean we should give them a break.

the implication would be that amazon is not responsible for the sale of bombs unless someone complains that they explode

I'm with you on that. If they removed the product once they learned what it was, I'm not sure how an you could say they "let" someone sell it, rather than that they were tricked into selling it for a while. The name of the show is The Great Amazon Heist, which maybe tells you a little bit about what is going on. I agree with the article, and perhaps with the prankster, that Amazon didn't do enough due diligence on the products they sell, but "let" implies they would continue selling it even after knowing what it was.