Buyers must prioritize Battery Health (State of Health - SoH) and Remaining Capacity, as the battery accounts for a significant portion of the vehicle's value. Request a Tesla Battery Health Report or use third-party diagnostic tools to ensure degradation is within acceptable limits (typically less than 10-15% for vehicles under 5 years). Additionally, verify the Drive Unit functionality, Autopilot hardware version (HW 2.5, 3.0, or 4.0), and the Infotainment Processor (MCU1 vs. MCU2), as these significantly impact the vehicle's performance and resale value.