Many consider the only way to validate is by having someone pay money for it. Lots of people (myself included) will say they will pay for something but when the time comes to buy they don't.
The book The Mom Test also points out well that lots of people will say your idea is good even when they have no intention of buying. They don't want to be assholes so they lie to you to make you feel good.
The real question is, how often are you signing away all of your intellectual property to your employer. Honestly, I've never had that in a single contract.