The contractor shall deliver to the buyer, or mail to him, at his address shown on the home improvement installment contract, an executed copy thereof completed in accordance with the provisions of this act. Until the contractor does so, the buyer shall be obligated to pay only the cash price. Any acknowledgment by the buyer of the delivery of a copy of the contract shall be printed or written in a size equal to at least ten 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 acknowledgment, conforming to the requirements of this section of delivery of a copy of a contract, shall be presumptive evidence of such delivery and of compliance with this section in any action or proceeding by or against an assignee of the contract without knowledge to the contrary when he purchases the contract.