Final answer:
Title insurance policy provides the best assurance of clear marketable title for a buyer.
Step-by-step explanation:
The best assurance of clear marketable title for a buyer of real estate is provided by a title insurance policy. Title insurance is a type of insurance policy that protects the buyer from any potential defects in the title of the property, such as liens or claims that may arise after the purchase. It ensures that the buyer has a clear and marketable title, giving them peace of mind and financial protection.