Have the completed Business Certificate form notarized. A sales agreement for buying a business is necessary for keeping both the parties on the same page and avoiding any legal trouble.An asset purchase agreement is a legal document used when buying or selling a small business. Read on to understand the basics. The Asset Purchase Agreement Checklist outlines important considerations for buying or selling a business, including assets, liabilities, and contracts. In an asset purchase, the purchaser only acquires the assets and liabilities it identifies and agrees to acquire and assume from the seller. You will need to fill out Form SS-4, the application for employer identification number. Wholesale and retail merchants without a business location in the City of Suffolk are exempt from this requirement.