The eyes of a vengeful man miss few details he can turn to advantage.
“Robinton” in the novel Dragonquest by Anne McCaffery
Angry and disgruntled customers are often times the most observant and critical. Ideally, you can take what they are saying and make use of their feedback to recognize and fix issues they are reporting. Aside from correcting problems and concerns these updates may also turn the tide in the customer’s view of your product offering.