During the Great Recession, I flew to another city and went through the extensive interview process. They hired me. Then, they just never gave me a start date. I asked and asked and asked. They got all squirrely and steadfastly refused to give me a date on which to show up and start work even though they had already hired me. That was 2008. I'm still waiting for that start date.
The unprofessionalism goes both ways.
Have similar stories.
My rule is until I have a signed start date, I do NOT turn in my notice.
Had one employer dump me because of that, only to find out they strung one guy along for months.