1. Start with observation
Document the symptom and its history, and take reasonable precautions if there's a safety issue.
2. Evaluate before specifying
Equipment condition, duct leakage, airflow, humidity, insulation, electrical capacity, and comfort by room all factor in before equipment gets picked.
3. Write the scope down
Preparation, protection, access, permits, testing, cleanup, finish restoration, exclusions, and change-order terms should be explicit, not assumed.
4. Compare what's actually proposed
Verify credentials, then look at the reasoning and boundaries behind each bid rather than just the total.
5. Confirm the job is actually closed out
Testing, cleanup, documentation, warranty terms, and ongoing maintenance responsibilities should all be confirmed before calling it done.