Everyone is going to get nasty emails and negative feedback at some point while selling on Amazon, and even when it is not your fault you are going to want to take care of it as quickly as possible. It goes without saying that the more orders you ship out the more opportunity you have for negative feedback to be left on your account.
After selling on Amazon for the past 13 years I have found there are a few things you can do to help keep nasty emails from turning into negative feedback, and to help you persuade a buyer to remove any negative feedback they have left on your account.
Contact the buyer ASAP, my advice is to respond within 24 hours or quicker, to let them know that you noticed and appreciate their feedback. Let them know you will be looking into the issue and will be contacting them again shortly. Making contact with the buyer quickly lets them know that you take customer complaints...
You are really close to getting actionable info to help you take your business to the next level or to start one from scratch.