Ask HN: Selling with powerpoint but without product

Myself and a friend were discussing the possibilities of selling a somewhat complex software product, which would be specialized toward a select few clients. The product does not exist, and such I argued that we couldn't sell it. My friend, who is a long term sales guy, argued that we could: By designing how it would work and present this to the potential clients.

I have tried this scenario before where I had only a prototype, and a very enthusiastic sales person went out and sold it to multiple clients. In this case however, we're talking about not a single line of code being written.

Personally I think it's a bit dodgy, i.e. It's a bit too much pie-in-the-sky to sell something that does not exist in any form other than as an idea. I have a hunch though that it is more common than I'd like to think.

I'm wondering if anybody here on HN has any experiences with non-existing products being sold purely on presentation? When it happens, is it an oddity or is it indeed pretty common in the IT industry?