If you've made an agreement with the buyer that he/she will get the smog test done on your behalf before they purchase the vehicle, perhaps this can be done. However note, the law requires the seller of a vehicle hand over to the buyer, at the time of purchase, a passing smog certificate. The sale "legally" can not be performed unless the vehicle's title is accompanied by a valid smog test certificate, title (duplicate allowed is original is missing), and bill of sale.