The sales contract is a document that is intended to show proof of ownership transfer for an object, and is required to make the vehicle road-legal in your respective country. 

The details it provides are:

• Who is the seller
• Who is the buyer
• What is the sold object
• What is the selling price
• Date
• No commission on it

Please note that the selling price on the document will show the top bid of the vehicle. 

You can see an example of this document here.