Bring the original diagnosis if you have it.
Photos, written estimates, model numbers and the exact reason given for replacement can help the second technician understand what was already found.
Ask for the diagnosis, not just another price.
A useful second opinion should help confirm what failed, whether repair is reasonable, and whether replacement addresses the actual problem.
Compare scope as well as equipment.
Two quotes can look different because one includes ductwork, electrical work, drainage, controls, permits or other installation details that the other omits.
Ask how the replacement size was chosen.
A like-for-like equipment swap is not always the same as evaluating the home and comfort needs.
You do not have to decide during the visit.
A good second opinion gives you clearer information so you can compare options, not more pressure.