>>That's not my experience; I now avoid asking hypotheticals because the results for me have been very unreliable.
The point in this context is that, while it may still be unreliable, it would be more reliable than simply asking if they like your product. And it is the best you can do, since no one is going to actually pay for a product that doesn't exist yet.
People pay for products that don't exist all the time. That's what contract software development is all about, for example. Ditto vaporware, Kickstarter, and "coming soon" features of existing products.
And, as mentioned elsewhere, people can think they are about to pay for a nonexistent product. Once you have proven willingness, there are a variety of ways you can finesse the issue of not actually having a product.
The point in this context is that, while it may still be unreliable, it would be more reliable than simply asking if they like your product. And it is the best you can do, since no one is going to actually pay for a product that doesn't exist yet.