AWS are not looking at customers data as it would be professional suicide. It would only require one disgruntled employee to leak this. Realistically they don't even have to as a proxies version of this data can be bought.
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.