There's the famous LATTE method that Starbucks uses.
L - Listen to understand the issue being presented to you.
A - Acknowledge by showing the customer you understand their grievance by verbally confirming it.
T - Thank them for letting you know about the issue.
T - Take action to resolve the issue. Turn the bad experience into a positive one.
E - Encourage them to return and build loyalty.
Another tip is that you have to separate yourself(mostly your ego) from the objective nature of the request. I build products for a living and when a customer tells me something is garbage or unusable, that can hurt my ego. But there's truth in everyone's perspective. You learn from it, you see the perspective, and you take action to improve it a little more for the next time.