I can't imagine an engineer creating a Diesel engine designed for fraud. But it happened. I'd say that in a company with an aggressive business culture like Amazon this is only more likely.
On the downside, they could lose their most profitable business unit.
Check out all the audits they go through. If you're an enterprise customer with this concern you can get access to those audit reports and see if it's one of the things being looked at by an independent third party.
Besides, all Target has to do is encrypt the data. Boom, non-factor.
It doesn't have to be a careful CEO decision. It could just be a curious engineer and someone in strategy who appreciates the data. That's probably how it started at VW, not with the board deciding that this is a wise strategy.
I am not saying that the Amazon board will authorize a change in strategy to dig into every customer data. But if I believed that companies internal audit were enough to prevent fraud, there would be no need for a banking regulator for instance.
I think it's totally healthy to maintain paranoia about AWS if you are competing against them.