I've found Glassdoor reviews to be very helpful. It's a great sign to see positive patterns like supportive management, good pay, work-life balance etc. On the flip side, red flag phrases like toxic leadership, frequent layoffs, low morale, high turnover... run for the hills.
To a certain extent, you can also suss out subtle red flags in the interview. When it was my turn to ask questions in a county govt interview this Spring, I asked what characteristics would make for a stellar incumbent. They let it slip that the position required a heavily independent workload with little support and lots of "figuring things out." No thanks - I don't thrive in that kind of siloed environment. Didn't get the job anyway.
As for bad boss stories, I had one in what was an otherwise decent organization. Fed supervisor with a heavy NY accent who did no work except filing multiple EEO lawsuits. She would waste the days away talking to whoever she could corner, repeating the same stories over and over, including her "unencumbered" house on "Lawng Island." Then she would pause for emphasis and say, "You know what that means? No mortgage!" and cackle. She's since been reassigned into a corner, but still.