The purchase agreement with the buyer, the seller agrees to surrender to the thing that is the subject of the purchase, and allow him to acquire the right of ownership to it, and the buyer agrees to that thing takes over and pay the purchase price to the seller. Under the contract, the contract shall be deemed always to supply consumer goods to be manufactured or produced. If the parties have the will to conclude the purchase contract without the determination of the purchase price paid for the purchase price agreed upon, which is the same or a comparable course at the time of conclusion of the contract and under similar terms and conditions usually sells.