Be very careful about how you ask questions because some forms of question solicit "approval" answers. It's culturally informed, some cultures try very very hard NOT to have to deliver a negative.This is one of those things that Steve Blank tries to address with the "Million dollar question." He suggests something like this (paraphrased from memory)
1. Ask your prospect (this assumes you've identified a prospect and gotten in the room, or at least on a call, with them) "If this product were available today and I offered it to you for free, would you start the process of deploying and roll it out immediately?"
If the answer is "no" then you clearly have bigger issues to deal with, considering you're offering the product for free. At this point you have to dig in and find out why. Maybe it's the case that while the current need is valid, there are simply higher priorities for the customer right now. In which case, your only issue is timing. But you may keep digging and find that there's something else. Anyway, repeat this with a few prospects, and you should start to converge on a valid understanding.
2. If the answer to question 1 was "Yes" (and I mean a solid "yes" not a bunch of hemming and hawing) then you next ask "OK, what if I charged you a million dollars for the product?"
Now... if the answer is still "yes", well, in that case you better have a purchase order ready to drop on your customer's desk Right Now. You've won, there's nothing left to do. Well, except for actually delivering the product, and successfully deploying, and integrating it, training users, creating value, etc. But in terms of sales, that would be the "Holy Shit" moment.
Probably not gonna happen though. Probably they'll start hemming and hawing and going "Well, uh... I mean, I dunno, a million dollars is a lot of money...", etc. That's OK. That's not a "no", it just means you now have an idea that the value your product represents to a customer is somewhere between 0 and a million dollars. If you find yourself in this situation, the (huge) body of material out there on sales, pricing and negotiation comes into play. But assuming you can get your customer to a "yes" at a number that would be profitable for you, then you now know that you have a product that can be sold to at least one customer for a profitable price. If you get this far, you're in pretty good shape. If the product actually exists, go ahead and sell it. Use the money to fund further exploration. Keep iterating. If it doesn't exist yet, promise the customer you'll let them know as soon as it's ready and keep iterating. Asking for a non-binding letter of intent to purchase might be useful if you're going to seek external funding.