[croissants]

If you're debating whether to go to school x and work with professor y, make sure you get a chance to talk to students who work with professor y, and ideally students who work adjacent to professor y. In my experience, bad advisors usually have students who will tell you that the advisor is bad (especially if you talk to them in person or over the phone, where there's no written record). If the students themselves are too scared, their friends probably aren't.

Any good program will have a built in process, for example an admitted students event, with this kind of interaction. Any good advisor will encourage you to talk to their students. If not, that is already a red flag.

Talk to current and former students! I was fortunate to have a great advisor, and I was always happy to talk to admitted students.