The due diligence period is the stretch of time, written into the purchase contract, when the buyer gets to verify what they are actually buying: physical inspections, a title search, reviewing leases and the rent roll, checking permits and zoning, and lining up financing. How it is structured varies by state and contract — some markets use a single due diligence window with broad exit rights, others use individual contingencies for inspection, financing, and appraisal, each with its own deadline.
For an occupied rental, due diligence is where investors earn their keep. Verify the rents the seller claims against actual deposits and signed leases, request estoppel certificates from tenants, confirm who holds the security deposits, and walk every unit — not just the vacant one. Deadlines in this period are usually hard: miss one, and the right to walk away with your earnest money can quietly expire.