I also point out when a requested feature actually exists as a whole company.
Pointing out that Product XYZ has 3000 employees and has been carving out a niche since 1995, while there are six of us with no knowledge of that market, is usually the only thing that gets him to accept that just because he understands what something does, it doesn't mean he understands what it takes to build it.
Just make sure you have infinite money first.
Maybe they are just looking for a side hustle.
This is how we used to sell drugs in college. It was a simple URL you could go to with pricing and you just sent texts to a burner phone to arrange a transaction.
But a virtual marketplace .. where different actors make transactions, is a different story. Consider you have a bug and people loose money because of you. It really needs to be solid.
Well, after a while they understood, there is a small difference, between a website - and a virtual market place.
Seriously, it is easy to forget, that for most people, all these technical things - is just dark magic in a black box. Which sometimes work and sometimes won't. And I find this sometimes hard to deal with, because society gets more and more technologized. At least a very basic understanding would be helpful.