Welcome to Bill-of-sale.org. Your document should include both "evidence of purchase" and "evidence of sale" with respect to the sale of goods or property. In some states, it's compulsory by law to state the sale as income on your tax return. Undeniably, it's a legal document between a seller and a buyer. It is the transfer of possessions or property for an amount of money and substitute of something of value and worth. When you agree to buy certain goods you should always check that it's free and clear of a mechanical lien. If it's got a lien on it, by law, it should be noted on the form.