In a proceeding under this chapter, it is a defense if proven by the defendant by a preponderance of the evidence that, at the time of the offense:

(1) The conduct alleged was authorized by the rules of professional conduct or the admission to practice rules for lawyers as adopted by the state supreme court, Washington business and professions licensing statutes, or rules adopted by the secretary of health or the director of licensing;

(2) The payment was an incidental nonmonetary gift or gratuity, or was purely social in nature;

(3) The conduct alleged was an exercise of a group-buying arrangement;

(4) The conduct alleged was a legal provider paying a service provider's bills from the proceeds of an insurance claim that included the bills;

(5) The conduct alleged was a legal provider paying for services of an expert witness, including reports, consultation, and testimony; or

(6) The conduct alleged was a service provider's purchase of advertising from an unrelated business that provides referrals from advertising for groups of ten or more service providers that are not related to the advertising business and not related to each other.