I used to puzzle over why potential clients who reached out to me always seemed to get more interested in hiring us if I tried to dissuade them by asking challenging questions. I think the biggest reason is that pushing back demonstrated that I care.
This seems bizarre. I work in sales, and I avoid making things too challenging for potential clients. Pushing back on the scope is one thing, but I think the way to show that you care about a potential client is to listen, identify their issue, and provide them with a solution that meets their budget. So many sales people try to push the envelope, to maximize the sale, for better or for worse, but I've never done that.