It is always a good idea to write a bill of sale when ever you sell your work or a possession, especially a motor vehicle. A bill of sale is important when ever you sell or buy a car. You can write a bill of sale yourself. Be sure to include all the details of the item sold, like in case of a motor vehicle; include the model number and the year of manufacture too. Writing the VIN number etc is also important. Mention the owner's name, new owner's name. Make sure you write complete legal name of the former and the new owner. The date of sake and the amount of transactions are a must. Signature of the old and new owner is important. After the document has been signed by both the parties, getting a legal stamp by the concerned law office or authority will legalize the bill of sale.