If the purchaser fails or neglects to pay, satisfy and discharge at maturity any taxes, assessments or other charges or encumbrances which shall be a lien upon the property being purchased from the board, or any part thereof, or any taxes or assessments levied or assessed upon the land so bought or the interest created by the contract or purchase of such property, or if the purchaser fails or neglects to keep the buildings and other permanent improvements upon such property insured as provided by this chapter, or if the purchaser fails or neglects to keep in good order and repair all buildings, fences and other permanent improvements situated upon such property as provided by this chapter, then, and in any such event, it shall be lawful for the board to pay, satisfy, discharge, settle or compromise such taxes, assessments, charges or encumbrances, or to insure said buildings, and permanent improvements, or any of them, or to do or cause to be done the work and supply the material necessary to keep the buildings, fences and other improvements situated upon such property in good order and repair. All monies so expended by the board shall be added to the selling price of such property, or balance due, and bear interest at the same rate as the original loan, or the current rate set by the board, at the board’s discretion, computed annually, from the date of expending the same, and shall be repaid by the purchaser to the board on demand. The board may amortize the repayment of such expenditures or permit repayment in installments upon such terms and conditions as it deems proper. The board shall be the sole judge of the legality or validity of such taxes, assessments, charges or encumbrances and the amount of insurance to be placed upon the buildings, and other permanent improvements situated upon such property and the amount necessary to be paid for the premiums for such insurance, and the necessity and nature of the work necessary to keep the good order and repair and the amount necessary to be paid therefor.