If a buyer contacts you with an issue, respond quickly and try to resolve the issue with the following:
Presume good faith. Don't start a dialogue by assuming your buyer is behaving unfairly or unreasonably. Problems are often the result of simple miscommunication or mistaken assumptions.
Set a constructive tone. From the start, make it clear to your buyer that you view the situation as resolvable. They’ll usually reciprocate, and you'll work out the vast majority of problems.
Focus on the problem. Talk about the situation you want to resolve and about potential solutions – not your assessment of the buyer's character. It may feel temporarily satisfying to "tell off" the buyer if you think they've acted in an inappropriate manner, but it almost always makes the situation more difficult to resolve.
Look for creative solutions. Try to find solutions where both you and your buyer get what you're looking for. If you sell the item at a fair price and the buyer gets something they want, both of you can go away happy.
Don’t forget the bigger picture. Keep your perspective and you'll be much better off in the long run.
Remember customer service. Customer satisfaction is good business. Being accommodating to your buyer can be better for your business in the future. Your reputation is your most valuable asset.