always apologies even if you don't see their side, one thing i have learned with being in customer service is that most ppl that complain are just having a bad day and want to vent and well sometimes you get the negative feed. they just want reassurance and to her they are right sometimes. So start with apologies, then listen to their complaint .Key rule is not to interrupt if you do this verbally, and be positive and upbeat with your response

I always listen to their concern and try to work things out. If they are not willing I politely tell them I’m sorry that I can’t help them with their needs and part our ways. I never try to hold a deal together just for monetary gain. It’s not good for all parties involved. Can’t win them all, and that’s ok! 

Best Wishes! 

Every situation is different as are individuals, however it is important to be kind to the individual and make sure you focus on facts rather than interpretations or assumptions of people’s motives. Apologize that the person believes they have been offended at your actions, but redirect to the facts. If you are wrong correct it. Be sure to always keep your customer’s best interest as the most important.

Step 1: figure what the true concern is.

Step 2: figure out what is within my control and take any corrective action that I can

Step 3:  always be willing to apologize and thank him/her for giving me the opportunity to make it right

Step 4: establish new protocol so that doesn't happen again

Step 5: If steps 1-4 don't fix it; then I offer to shake hands and part ways amicably. 

Bottom line:  Never burn a bridge.

Stay positive and focused

It depends on the situation, however you always want to hear the complaint and then offer what solutions best fit that situation

I Would correct the mistake and would most likely refund the money.  I would also make sure they were pleased with the final outcome.

I would find out what their issue was and do everything I could to resolve it. 

with kindness, dont take it personal. then of course depends on what you mean by negative

My first step if that happens is to make the customer happy. Often this is a failure to set expectations properly. If this happens I do WHATEVER I can to change this customer to make them happy and change their point of view. If that doesn't happen, after several tries, I walk away. As a small business owner we have to worry both about profile and loss and time.  I hope that helps.