In my last role, I worked at a busy restaurant, which ranked consistently in the top 25 of all their stores out of 250+ managing the bar staff. On a daily basis, I'd be the one answering all the emails we'd receive from customers concerning their comments or complaints. If there was a problem, I always offered to call them to talk about it and help rectify the issue. Having that personal touch, inviting them back in with dinner on us, helped us retain almost 100% of our customers who had a problem. People just want to be heard most of the time. They want someone to recognize that a mistake was made and to have it corrected. I've received some very angry emails in my day, but once I responded or got them on the phone, I was always able to win them back to our side.