Wis. Stat. § 452.134

(1) Agency relationship not required. (a) Subject to par. (b) , a broker may provide brokerage services to any person in a transaction, whether or not the broker has entered into an agency agreement with a party to the transaction or the broker has been engaged to provide brokerage services in the transaction as a subagent. (b) A broker may not negotiate on behalf of a party to a transaction unless a party to the transaction is one of the following: 1. The broker's client. 2. A client of a principal broker who has engaged the broker as a subagent.

(2) Multiple representation relationships; consent required. A broker may not provide brokerage services in a multiple representation relationship unless all of the broker's clients in the multiple representation relationship have consented to a multiple representation relationship in writing.

(3) Designated agency; consent required. (a) A broker in a multiple representation relationship may not engage in designated agency unless all of the broker's clients in the relationship have consented to designated agency in writing. A client may withdraw consent to designated agency by written notice to the broker at any time. (b) If a broker is engaged in designated agency, the broker's employee who is negotiating on behalf of a client of the broker in the transaction may provide to the client on whose behalf the employee is negotiating information, opinions, and advice to assist the client in the negotiations, whether or not the information, opinions, and advice place the interests of one of the broker's clients ahead of the interests of another client of the broker.

(4) Multiple representations relationship without designated agency. If a broker's client in a multiple representation relationship does not consent to designated agency or withdraws consent to designated agency, the broker and the broker's employees may not place the interests of any client ahead of the interests of any other in the negotiations.