Getting people to believe error messages is surprisingly hard. "The server says I used the wrong certificate - what am I supposed to do here, what went wrong?". 9/10 times they used the wrong cert, and the rest of the time they forgot to register it to the right app. But they don't trust the errors...
People with exposure to tech support often complain that users never read error messages. It's almost understandable for low-skill users. But it's surprising and disturbing how many professional developers also don't read error messages.
Error messages can be wrong or misleading sometimes, but how do you not at least think about what they said and if that could actually be what's wrong?
So I updated my test to grab their OS user name and called them.
"I thought you were testing something so I didn't call"
While they may read the message, it didn't mean the purpose was clear.