The walkaround: what a good detailer checks before quoting
A serious detailer does not quote a paint correction from a photo. The first diagnostic is a paint depth gauge — a small ultrasonic or magnetic device pressed against each panel that reads total paint thickness in microns. Factory paint typically reads 100–160 microns. A panel reading 250 microns has been resprayed; a panel reading 80 has probably been machine-polished hard before and has little clearcoat left to work with. Correcting paint means removing clearcoat, so knowing how much remains is the difference between a safe polish and striking through to the colour coat.
Finally, they will inspect under proper light. Swirls, buffer trails from a previous bad polish, water-spot etching and bird-dropping etching all look different under an inspection lamp, and each needs a different fix. Water spotting deserves a special mention here: sprinkler overspray and mineral-heavy washing water leave alkaline deposits that, baked at 70-plus degrees, etch physical craters into clearcoat within days. If a detailer points these out during the walkaround rather than discovering them mid-job, you are dealing with someone who has priced the work honestly.