(3) Each certification of a county or city and county shall be valid only until the next survey made by the board. If a county or city and county has been certified following a survey that includes a sampling of assessments, the board may continue to certify that county or city and county following a survey that does not include sampling if the board finds in the survey conducted without sampling that there are no significant assessment problems in the county or city and county. The board shall, by regulation, define "significant assessment problems" for purposes of this section, and that definition shall include objective standards to measure performance. If the board finds in the survey conducted without sampling that significant assessment problems exist, the board shall conduct a sampling of assessments in that county or city and county to determine if it is an eligible county or city and county. If a county or city and county is not certified by the board, it may request a new survey in advance of the regularly scheduled survey, provided that it agrees to pay for the cost of the survey.