I've been around the horn a few times on this. Anything short of a commitment to pay for the product (up to and including prepayment) is just noise. It's not so much that people lie about what they say they would do, but that it's too easy for you to lie to yourself about the signal you're actually getting.

Here's a good example:

> Though a lot of people I spoke to sounded "excited", I got very few signups. (They're not my target audience, so I didn't ask them if they'd pay for such a product)

Those people weren't in your target audience, and you didn't ask them to pay, but I presume you take it as a positive sign that this particular audience was "excited." But it's not. It's not anything since they're not even potential customers. That's how we subtly deceive ourselves.

Talk directly to people in your target audience (contact on social, then move convo to email, then move convo to telephone) and try to get them to put some skin in the game. One popular tactic is to offer a free feature request for a refundable prepayment.