Check REPUVE before you buy
Before putting down a single peso, go to repuve.gob.mx and look up the vehicle's VIN. The system immediately tells you whether that unit has an active theft report in any state in the country.
This lookup is free and requires no registration. Copy the VIN directly from the registration card or from the metal plate usually on the dashboard, visible through the driver's side windshield.
If the seller resists letting you do this check, or makes excuses to avoid showing you the full VIN, that alone is reason enough to walk away — no matter how good the price looks.