Last time I got a job offer, the first thing I did was call up two people who'd sold their companies to that employer, one guy who worked there, one guy who'd quit, and one who'd been offered another job and turned it down. Next time I'll try the "scale of ten" trick, too.
All management positions are to some extent sales positions, and part of a good sales technique is to shape the truth so the good parts are obvious and the bad parts aren't. The more someone's naturally talented at this, the easier it is for them to fudge the truth.
This is much easier to accept if you consider it in the other direction. Would you really think it unethical to do this kind of due diligence on a prospective employer? Would your boss find it creepy? I was open about it.