Before you buy an existing business, find out if the business owes any Texas taxes. A purchase agreement is the written contract detailing all of the relevant terms of the business sale.Ready to start your asset purchase journey? A Business Purchase Agreement is a contract that transfers a business entity from its owner to a new buyer. Buying a business in Texas? Seller financing can help a buyer pay more for the business than if the deal were financed only through traditional financing sources. Texas Sales and Use tax FAQs about buying, selling or discontinuing a business.