Hilariously, they "destroy" your inventory by selling it and keeping 100% of the money.
I don't think that storage fees specifically are a racket. What do you want Amazon to do, store a bunch of non-selling products indefinitely for free?
The lesson is that you shouldn't send a ton of products to FBA unless you have good reason to believe they'll move.
Details for people not familiar with the Amz horror stories, please?
They ask for invoices from sellers to "prove authenticity", claiming that's the only purpose, then mysteriously the vendor named in the invoice gets a call from Amazon the next week trying to source the product.
They make their own private label products and put links to them on other sellers' product pages, giving themselves free advertising.