In one sentence
The municipal certificate confirming a building may lawfully be occupied for its stated use.
The longer version
The CO, or its local equivalent, evidences that the building passed inspections for its use classification. Older properties sometimes predate CO requirements, and municipalities differ wildly in recordkeeping, so a missing CO is common and usually resolved with a letter of no violation or municipal search.
For diligence, the CO cross-checks the zoning report and the rent roll: the certificated use should match how the property actually operates.
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