A retail seller or the holder of a retail installment contract may charge and collect a service charge in respect of a retail installment sale and may calculate such service charge in the manner and at the rate or rates specified in the contract governing the sale.

6 Del. C. 1953, § ?4315; 52 Del. Laws, c. 342; 62 Del. Laws, c. 228, §§ ?8, 9; 63 Del. Laws, c. 2, § ?16;