The closest I had to a problem was when I sent an email stating that a product is not functional after a year and a half. They replied that the 30 days return window is over and that I should contact the producer.
I replied that according to the law, I have 2 years of warranty with zero costs from my side. They replied that are very sorry for the misunderstanding (or something like that), together with a return slip.
Teh second one would probably be when I was suggested to test Amazon Prime and I was charged 50€ right away. I replied this is a test. They replied that I actually signed for Prime, that it was not a test.
To what I replied it was, to what they replied they will reimburse me 50€ minus the fast shipping costs (that would otherwise be included in Prime). To what I replied i was really unhappy. To what they replied that 50€ are on their way to may credit card.
This is one of the reasons I buy with Amazon without much fear.