Earlier quoted context omitted.
There's an entire book on this I read a few years ago, let me find it
Is it https://www.momtestbook.com/ ? That's a good one.
Essentially the observation was the same. A person claiming they'd buy something is worthless information. He had some strategies for getting around it that I've long since forgotten.
It's apparently not on archive.org yet. I just dropped my copy into my next donation box. It'll be there eventually now.
The term he used was "pretotyping" that term will probably yield everything you need.