1) Evaluate the validity of their feedback. Are they simply trolling, or is this an actual experience a customer is facing that is worth addressing? 2) Document, categorize, and archive their feedback for further analysis to add to the "big picture" for how our organization can improve. 3) Thank the customer for their feedback, and acknowledge that it has been documented to further improve our business practices. If the experience warrants an apology, offer it sincerely with the intention that it should be addressed.