Three clerks were cited for selling beer to an underage operative during an undercover beer-buying operation in the city and county.“We sent a 19-year-old operative into several stores to attempt to purchase alcohol,” said McMinnville police investigator Capt. Derwin Adcock, noting the department does such checks regularly. “He was able to purchase beer in two markets in the city and there was one in the county.”State law requires clerks to check IDs of all persons asking to purchase alcohol regardless of their apparent age.Adcock said letters were sent to 15 stores in the city limits which did not sell to the operative, commending them on following the law. Those markets that did sell, however, could face civil penalties in addition to the penalties given to the clerks in criminal court.