I think the point is that those are the clients you don't want, so you encourage them to select themselves out of working with you. The fact that it might be bad for their own business is not relevant to you as a consultant.

I think it's normal for non-technical people to have no idea of how things work and of what to expect. It's our responsibility to communicate. And, within reason, theirs to listen.

This can only happen if they have reason or motivation to trust the expertise, and an expectation that the relationship can be fruitful.

Like you said, they must at least be willing to listen.