Some dealerships may offer a brief grace period (usually a few days) allowing buyers to change their minds, but this is at the discretion of the individual dealership and is not required by law in South Dakota. If a dealership does offer a cancellation period, the terms (such as any associated fees or restocking charges) will likely be outlined in the sales contract.
Therefore, the ability to return a car within 30 days and obtain a full refund depends on the specific policies of the dealership where the vehicle was purchased, not on a state-wide law in South Dakota. It's essential to carefully review the sales contract before signing to understand the dealership's cancellation and refund policies and any applicable deadlines.