Let me start by saying I love the community here and have always found Ask/Show HN threads some of the most informative.
I got the standard approach a few days ago: an acquaintance with zero technical ability (who actually said he's "not good with the computer codes") approached me regarding something I should build in a field of shared interest which is ripe for technical disruption.
What surprised me is that it's actually a really good idea, and I could see it being a viable business - not the Next Big Thing, maybe not even a startup by traditional HN definitions (there would never be massive, viral growth), but I could definitely see it supporting a small staff if executed properly.
Here's my question: I could build it, but I don't know what this prospective cofounder would do. He's not a salesman, he's no more of a domain expert in this field than I am, and he's not a business guy (CPA/forensic accountant by trade); he's only marginally better connected than I am in the field as well. That being said, is there some vital function I'm missing out on? How can I vet him without just coming out and saying "what good are you?"
If your acquaintance is OK taking a back seat for the first iteration, then I think your problem is solved. If not, then you should have a frank discussion about what each of you will bring to the table. Even small businesses are a ton of work. At a minimum, you could offload the less technical work so that you can stay focused. Perhaps he focuses on connecting with the customer while you build the prototype? Most founders underestimate the value of connecting with the customer in the early days and in turn don't allocate enough of their time/energy to this task.