You’re wondering who is responsible to smog check a car when you’re selling it. In most states, the law says that if the car is less than four years old, a smog test won’t normally be required, and a fee will be charged to the buyer. If the car is older than four years and was smogged within 90 days prior to the sale, no smog check is required. For cars more than four years, but less than 30 years old, a smog check will be required of the seller. Cars more than 30 years old don’t require smog tests upon title transfer.