Theranos was worth $9B in 2013 money, and it latet turned out that they had literally nothing but hype. Enron was posting $100B revenue the year before it went bankrupt. Bernie Madoff's fund had huge banks as institutional investors. Magic Leap was valued at $4.6B and had some purportedly amazing demos behind closed doors that anyone who witnessed them thought would revolutionize entertainment.

While these are not necessarily typical cases, they show that it's absolutely possible to have gigantic valuations raised from industry experts with nothing to show for it, if you're good enough at lying.