Have you ever heard of the saying 'don't bite the hand that feeds you'? This can be applied to how you treat your customers. Customers who take the time to complain are also taking the time to state what went wrong with your processes, product or communication, and this effort should be acknowledged and acted upon. Afterall, fixing the problem for one customer can also help many others, including the ones who never contacted you.
Based on research from contact centres throughout the UK, this report from ContactBabel looks at: