Most often peoples ideas pretty much require a server and a much more complicated pricing scheme than they think. When that's the case I explain that much, but you probably always loose when you do.

One of the most awkward moments was when I actually met with a friend and his friend about making an app. I only realized halfway through that they didn't have an idea, just a wish to make an app. A few hours of awkwardly groping for some tenuous b2b projects and we parted company.