The planning board shall file a recommendation and report with the county commission. The scope of review by the county commission shall be limited to the recommendation and report of the board; except that the county commission may hear and consider additional evidence, if the county commission finds that the evidence in the exercise of reasonable diligence could not have been produced, or was improperly excluded at the hearing before the board. The county commission may in any case hear and consider evidence of alleged irregularities in procedure, or of unfairness by the board, not shown in the record. The county commission in determining the result reached by the board shall give due weight to the opportunity of the board to observe the witnesses and to the expertness and experience of the board. Whenever the county commission finds there is competent and material evidence, which in the exercise of reasonable diligence could not have been produced, or was improperly excluded at the hearing before the board, the county commission may remand the case to the board with directions to reconsider the same in the light of the evidence. The report shall consist of a complete transcript of the entire record, proceedings and evidence before the board. The county commission before deciding the case shall personally consider the whole record, or such portions thereof as may be cited by the parties, and shall personally consider any oral or written arguments presented by all interested parties.