includes the reasonable cost, as determined by the Secretary of Labor, to the employer of furnishing such employee with board, lodging, or other facilities, if such board, lodging or other facilities are customarily furnished by such employer to his employees: Provided, That the cost of board, lodging, or other facilities shall not be included as a part of the wage paid to any employee to the extent it is excluded therefrom under the terms of a bona fide collective-bargaining agreement applicable to the particular employee: Provided further, That the Secretary is authorized to determine the fair value of such board, lodging, or other facilities for defined classes of employees and in defined areas, based on average cost to the employer or to groups of employers similarly situated, or average value to groups of employees, or other appropriate measures of fair value. Such evaluations, where applicable and pertinent, shall be used in lieu of actual measure of cost in determining the wage paid to any employee. In determining the wage of a tipped employee, the amount paid such employee by his employer shall be deemed to be increased on account of tips by an amount determined by the employer, but not by an amount in excess of 50 per centum of the applicable minimum wage rate, except that in the case of an employee who (either himself or acting through his representative) shows to the satisfaction of the Secretary that the actual amount of tips received by him was less than the amount determined by the employer as the amount by which the wage paid him was deemed to be increased under this sentence, the amount paid such employee by his employer shall be deemed to have been increased by such lesser amount.