Commercial policies are treated differently than personal lines insurance. Personal lines insurance is prorated over the life of the policy. With Commercial there is a financial penalty called a short rate.
This is incurred when the insured cancels an insurance contract prior to the expiration date of the contract. This is generally a minimum earned premium of 25% of the policy plus taxes and fees that are fully earned ie non-refundable when the policy is issued.
So if you cancel your policy 30 days after it is issued, you will be entitled to a refund but the amount will be subject to the balance of the minimum earned premium and taxes and fees.