This had not occurred to me believe it or not. I like the idea, but one thing that's missing is a way for service providers to prove their answer is satisfactory without the user stiffing them by saying "I went with someone else". Since the question is arbitrary I don't know if you could come up with a general proof.
probably nostr:npub1jlrs53pkdfjnts29kveljul2sm0actt6n8dxrrzqcersttvcuv3qdjynqn has the light to all these questions
Discussion
The problem is basically dispute resolution. Check this out https://github.com/BitResolve/Bounty-Adjudication-System
I don't think that needs to be solved tbh, at least not at first, it just might be that this is solved via generic npub (both customer and service provider) reputation
the service provider doesn't need to prove anything, because that'd be too costly at scale, instead, the incentive is aligned in that the npubs might want to transact again in the future.
i.e. if I'm a person buying a midjourney image, the image is great and I don't pay the service provider, I risk that that service provider (and others watching my behavior) will not serve me in the future
there is risk to the service provider, but that's up to the market/service providers to price/mitigate
the risk could be pushed to the user (e.g. via hodl invoices) but service providers are better positioned/have more incentives to mitigate risk than end users