Once you have determined the name of your business you will need to determine the Type of Business that you will file. A sales agreement for buying a business is necessary for keeping both the parties on the same page and avoiding any legal trouble.A seller must give all prospective purchasers Form TP153, Notice to Prospective Purchasers of a Business or Business Assets. An asset purchase agreement is a legal document used when buying or selling a small business. Read on to understand the basics. Anyone who will operate a business in Suffolk County under a name, other than his or her own, must file a Business Certificate with the County Clerk's Office. The Asset Purchase Agreement Checklist outlines important considerations for buying or selling a business, including assets, liabilities, and contracts. Both the seller and purchaser of a group of assets that makes up a trade or business must use Form 8594 to report such a sale.