If Amazon's public key is able to decrypt the gibberish message and turn it into sensible English, it indicates that the message was encrypted using Amazon's private key. This means that the message was likely sent by someone who possesses Amazon's private key, which should be a closely guarded secret. Therefore, seeing that the message can be decrypted with Amazon's public key should increase confidence that the message was actually sent by Amazon and not by someone else impersonating Amazon. It provides an additional layer of security and authenticity to the message, which can be especially important when dealing with sensitive or confidential information.