Making the most of unconstructive criticism

Angry customers are unavoidable, no matter how good your service. Some become so incensed that they start lashing out. They go on about how crappy your business is, promise to tell everybody else how crappy your business is, and vow never to come back.
As the service provider, it’s easy to become angry in return. Nobody likes feeling attacked, especially with claims that seem unjustified or overblown. You may be tempted to ignore these (hopefully rare) tirades and move on with your life.
Take the customer above. I see a lot to criticise about Hopscotch’s user interface and navigation flows, but he’s exaggerating our flaws a little. And even if you believe that everything happened just as he described, payment servers go down and customer service agents get busy, even at global, multi-billion dollar corporations. His claim that our site is terrible hurts, his plan to sink the reputation of a small business doing its best to serve him is unkind, and his suggestion that we rebuild everything from scratch is unhelpful. Had it been me dealing with him, he might have received a less polite response.
But to dismiss him would be too hasty. There are people who are never happy with anything, and he may well be one of them, but I’ll assume that he made his comments after several long, hungry, frustrating minutes spent trying in vain to order on our site. The tribulations that led to his anger, even if not the remarks precipitated by it, are worth paying attention to.
What he said also gives voice to those in the same boat who say nothing, but instead just leave without ordering. We have data on these people, but we have data on a lot of things. They come to life when they slap you in the face.
These are good reasons to thank him for telling us off.