Please also review the separate Contra Costa County or city specific Ordinances and Regulations for property in the area you are either selling or buying. This form is intended for use with the.Seller agrees to sell to Buyer, and Buyer agrees to purchase from Seller, subject to the terms, covenants and conditions set forth herein. Attachment 4-2: Addendum to Purchase and Sale. Agreement. Agreement to Sell and Purchase. Seller agrees to sell to Purchaser, and.