Here is what the Agency Relationship Disclosure states, the form that Aaron mentions below:
"If you desire representation you must enter into a written contract, according to state law (a listing contract or a buyer representation contract). Until such time as you choose to enter into a written contract for representation, you will be treated as a customer and will not receive any representation from the broker or salesperson. The broker will be acting as a Facilitator...."
As a Facilitator, the agent owes no fiduciary duties to the customer, except confidentiality. Where as a Seller's Agent or Buyer's Agent would owe the duties of:
Unless you enter into a signed contract for representaion, that agent owes you none of the above duties, and like state law says in the disclosure form, they are not "your agent".
So to answer your question, YES, if you want representaion, you are required by MN law to enter into a written contract with the agent of your choice.
If you would like to see these forms, let me know and I will email them to you!