The only reason merchants get any business on Amazon is that customers are at least partly protected by Amazon's support infrastructure.
I'm sympathetic regarding some of the more egregious stupidities Amazon has foisted on some merchants, but when it comes to this part, it's pretty unambiguously what you signed up for.
Consider it from the other end: If you were selling autonomously on your own site, would you treat customers this well? What does your answer say about you? What impact do you think your answer will have on potential customers' choices?
I'm sympathetic regarding some of the more egregious stupidities Amazon has foisted on some merchants, but when it comes to this part, it's pretty unambiguously what you signed up for.
Consider it from the other end: If you were selling autonomously on your own site, would you treat customers this well? What does your answer say about you? What impact do you think your answer will have on potential customers' choices?