This really depends on what the negative comment actually says. If someone is making a fair complaint about your product or service, you should respond seriously and try to help them solve the problem. Customers want to know you care about fixing things that went wrong. But if someone is just trolling or being rude for no reason, a light joke can show other people reading that you don't take yourself too seriously. Just make sure your humor doesn't sound mean or dismissive because that can make things worse. The goal is to look professional while also being human. If you're not sure, staying polite and helpful is always the safer option. What do you think is the right balance here?