Leadership
There are many ways of finding out a customer is not only complaining but also genuinely unsatisfied with your services. The tricky part is that by the time the complaint becomes explicit, the relationship is already damaged. A good lead should be able to sense dissatisfaction earlier than that — reading customer behaviour, understanding what they actually expected, and honestly assessing how far reality has drifted from those expectations.
Start with customer experience, not the customer
The first move as a technical leader, before approaching the customer directly, is to talk to whoever owns the customer relationship on your side. Account management, customer success, sales — whoever has been in regular contact. Go in with genuine curiosity, not defensiveness.