The seller shall deliver or mail to the buyer, at the address shown on the contract, a legible copy thereof completed, in accordance with the provisions of this chapter. Until the seller does so, the buyer shall be obligated to pay only the cash sale price. Any acknowledgment by the buyer of delivery of a copy of the contract shall be printed or written in a size equal to at least 10-point bold type and, if contained in the contract shall also appear directly above the space reserved for the buyer's signature. The buyer's written acknowledgement, conforming to the requirements of this section of delivery of a copy of a contract, shall be a conclusive presumption of such delivery and of compliance with this section and § 4306 of this title, in any action or proceeding by or against an assignee of the contract without knowledge to the contrary when the assignee purchases the contract.