(1) Upon every person engaging within the state in the business of providing real estate brokerage services; as to such persons, the amount of the tax with respect to such business is equal to the gross income of the business, multiplied by the rate of 1.5 percent.
(2) The measure of the tax on real estate commissions earned by the real estate firm is the gross commission earned by the particular real estate firm including that portion of the commission paid to brokers, including designated and managing brokers, in the same firm on a particular transaction. However, when a real estate commission on a particular transaction is divided among real estate firms at the closing of the transaction, including a firm located out of state, each firm must pay the tax only upon its respective shares of said commission. Moreover, when the real estate firm has paid the tax as provided herein, brokers, including designated and managing brokers, within the same real estate firm may not be required to pay a similar tax upon the same transaction. If any firm located out of state receives a share of commission on a particular transaction, that company or broker must pay the tax based on the requirements of this section and RCW 82.04.067.
(3) For the purposes of this section, "broker," "designated broker," "managing broker," and "real estate firm" have the same meaning as provided in RCW 18.85.011.