The county board shall have power to settle by compromise or by accepting in full settlement thereof less than the face or full amount on any claim, judgment or demand in favor of the county, on which said claim, judgment or demand no payment or payments have been made or recovered during a full period of five years from and after the date or dates on which said claim, judgment or demand became due and enforceable, and execute full acquittance or receipt for said claim, judgment or demand, or to sell, at public or private sale, any claim, judgment or demand in favor of a county for cash, at the best price obtainable in the judgment of said board, and execute and deliver a proper transfer or assignment of said claim, judgment or demand so sold; Provided, that no member of the board may be personally interested, directly or indirectly, in the purchase of any such claim, judgment or demand.