Earlier quoted context omitted.
Is there anything we could do to make you (and many more with the same sentiment) more comfortable? We are thinking of writing a blog post of what happens in the background would that help? Any other ideas?
There is absolutely nothing you could say or do that would make me give you my password. Also, I assume, you need to store it in the clear to use it. You claim to not have access to credit card information or being able to order something, but I already have to trust you to believe that claim. Also, Amazon could change their policies at any time -- after all you have credentials, Amazon could decide to trust you.
You will find that both are not possible