Which seller questions should I ask out loud at the vehicle?

Ask questions you can verify: Has this been diagnosed. When was that work done. Can I see the receipt. Who did the work.

Read priority questions from your list rather than improvising under pressure. Order matters when time is short.

Listen for consistency with the listing and with what you can see. A changed story is information.

A Captain's Report prioritizes these questions for the specific vehicle so you are not inventing them on the curb.