LEGALITY OF VARIABLE RATE SERVICE CHARGE UNDER WASHINGTON RETAIL INSTALLMENT SALES ACT So long as the maximum rate does not exceed that which is permitted by RCW 63.14.130(1) in those instances where that statute applies, the Washington Retail Installment Sales Act, as codified in chapter 63.14 RCW, does not prohibit a retail seller from imposing a variable rate of service charge in a retail installment contract for the purchase of a manufactured home.