This is why it comes down to trusting Amazon. Essentially the question is "Do you trust Amazon not to do something that would be 'professional suicide', like accessing a rival company's AWS data, enough to risk giving them your data?" If you're running an online retailer that's a competitor to Amazon you should probably fall on the side of caution because companies do stupid shit all the time.
- Amazon predatory pricing
- Amazon trying to mistreat their workers (including AWS) as much as they can
- Amazon/AWS copying products, FOSS software, and messing up with companies that they invest into.
- Their complicity with all the scams going on their store.
- And a big, big etc
But, but, Amazon is not AWS! Amazon is retail and is a different environment! Yes, but it is under the same people.
Doing that at scale doesn't make them more trustworthy. Or it shouldn't. Then again I guess if you're a super-creepy stalker at large enough scale then you're Facebook or Google and instead of getting probation and a restraining order you get billions of dollars, so maybe it does work that way.