Oh, I've experienced this, not with a fake buyer, but a fake partnership deal.
I was contacted by someone at CrowdStrike (yep, I'm naming those bastards), who wanted to setup a meeting about a potential partnership. We had a chat, and then had a long meeting with several CrowdStrike people, including some software engineers.
I demo'd our product, and all the way through, the devs were asking these really detailed questions - they wanted to know precisely how everything worked.
In my naivety, I assumed this was all in good faith, despite alarm bells starting to ring with some of the questions.
Anyway, all through the demo they went on about how great the product was, and sucked me dry of information - and then ghosted me. I reached out by email a few times after, and every time all I got was "yeah, we're busy, so...".
I learned a valuable lesson that day: don't assume others are as principled as you.