Unless a return option is written into the sales contract, a used car purchased in Illinois may not be returned to a dealership. This also applies to new car purchases. There is no "cooling off period" protection for car buyers.
Illinois has a "Lemon Law" designed to protect consumers from vehicles with factory faults of defective parts. This protection does not extend to used cars though. Without a prior agreement, the decision to accept a returned car is left to the dealer's discretion. A dealer may negotiate a refund, but this instance cannot be counted upon and is considered a rarity.