Every outdoor environment carries background mold spores. San Diego's background load shifts with season, wind direction and how recently it rained. An indoor count of 900 spores per cubic meter can be perfectly normal on one day and a red flag on another.
That is why every inspection we perform includes an outdoor reference sample. The comparison — indoor versus outdoor, by genus — is the actual test.
Visual-only inspections skip this entirely. They also miss the places mold actually lives: behind a dishwasher, in an attic above a bathroom fan that vents into insulation, in a crawl space under a slow supply-line drip.
If an inspector tells you sampling is unnecessary, ask them how they intend to distinguish normal background spores from an active indoor source.