Very true and a common pattern in Startups and even large companies. Sell what you don't have. Not sure it works out all the time, but it has for some.
I believe most enterprise shops sell what they don't have. But they also know by the time the customer is ready they'll have it built & ready. The customer is also aware of the current state and timelines.
For theranos and fyre festival. I'd say it was less playing timing to their advantage and more fraud.