Business Purchase-Sale Agreements. To learn more about how our business purchase and sales agreement lawyers can help you, contact us online or call our local law office at .A business purchase agreement is a legal contract specifying terms for buying or selling a business, including conditions and obligations. This particular contract dictates the purchase and sale of real estate in Phoenix and throughout the state. Purchase Agreement ; 2. This guide will help you write a business purchase agreement with the terms and conditions you need for a smooth sale. A Business Purchase Agreement is entered into between a seller and purchaser for rights to the business. The documents you need to buy or sell a business depend on the structure (discussed here) and complexity of the deal as well as its specific terms.