I think Dane Maxwell is one of the best at doing this.

He published a PDF guide here: https://thefoundation.com/wp-content/uploads/2020/10/Intro-t...

And there are many examples of him doing idea extraction online. While you can do IE via email/chat, phone calls or even in-person meetings are most effective.

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- Instead of quantity, go for quality. You just need a few good idea extraction sessions. (You may have to cold-call 100's of contacts before that first good session, though...)