Nearly everyone who curses in their first email will apologize upon receiving an email from the founder. They were probably just having a bad day and assumed that $Company was some corporate powerhouse trying to nickel and dime their customers.
There's about 5% of people who persist in nastiness.
But almost everyone ends up being happy about the interaction, many end up renewing their subscriptions, and some will even email other companies asking them to integrate our technology. Sometimes the root of the frustration was that our service didn't work better with other platforms, which is something we can't control on our own.
So having these very excitable folks sending emails on our behalf can be a powerful thing. It just requires biting your tongue instead of replying in the heat of the moment!
I try to remember this when I interact with people in any medium (including in-person). Snark/anger/sarcasm are often just the envelope for the content of a message. If you don't let it affect you, you can respond to the content of the message, not the delivery, and break down a number of walls instantly. And as a bonus you're not giving someone else control over your emotional state.
That said, some people are just abusive idiots and you kind of have to have a sense for when you're wasting your energy.
The angry tech customer generally cares about a problem they're trying to solve. The demanding restaurant patron is focused on the feeling of exercising power over someone subservient to them.
Any overlap between those groups of people is random.
The thing with real stores is that all the assholes are from this group. The ones that are having a bad day may react badly to something, but do not go out of their way to create problems.
What means that real stores have many fewer problem customers. But they can't count on them changing either.
The angry message to a tech service provider can often be a last ditch attempt at resolution. An angry review of a restaurant is usually little more than a public “fuck you”: they aren't getting further business from that customer.
Pictures of health code violations and stories of health code violations usually raise some red flags (especially if recent). Those are too easy to fake.
The most useful ones are when they go through exactly what they thought was right/wrong with the food (and a pattern emerges across the pictures and multiple reviews about different dishes).
If the restaurant is a 3.1, then yeah, try to find a different place - there IS hair in the food, the cockroaches are real and the waitress DID stick the hotdog up the you know what.