“Not interested.”
What it usually means: A reflex, not a decision. They've had no reason to listen yet, so no is the safest answer.
Try: “Totally fair, you don't know me yet. Can I ask one question before I let you go: [problem question]?”
Why it works: Agreeing lowers their guard, because there's nothing to push back against. One small question is easier to say yes to than a pitch, and a small yes is how attention starts.