Has Amazon ever used AWS to pressure potential competitors?

I have heard people suggest that relying on AWS could be a risky move for potential Amazon.com (e-commerce) competitors. The rationale seems to be that if Amazon wanted to, they could refuse AWS discounts or be less willing to support and cooperate if they deem someone to be a competitor. Some have even suggested that Amazon could access one's business-critical data on the back-end without having to disclose the access if they chose to, and so gain a competitive advantage.

The logic further goes that in order to avoid ending up in this hypothetical situation, one should not make use of AWS products and features which could be viewed as "vendor lock-in" and design one's systems to be "cloud agnostic". Or just avoid using AWS altogether.

My position has been that it is irrational to think that Amazon would a) even think of me as a competitor and b) put AWS' reputation at risk by employing shady tactics to sabotage my business. And that preparing for this (imaginary?) scenario would lead to missing out on or making ineffective use of AWS' (arguably best in class) cloud products. Or taking on significantly more complexity in order to be "multi-cloud". In other words, choosing to perform more "undifferentiated heavy lifting" on the basis of what seems to me like an irrational fear of being locked-in and taken advantage of by Amazon.

My question is: are there any documented cases of Amazon taking advantage of competitors via AWS in this manner? Does anyone here have (anecdotal) experience with such a situation that they'd be willing to share?