Hi first, Has the car been checked out by a Mech? If not take it tip do not hand any money over untill the car has been checked otherwise you will be very very sorry, regards the receipt, Date, day, month, Reg,Colour, make, CC, Petrol/derv, price, either cash or Cheque, Cheque No, Warrantee (If any) get the other persons Land line No + Mobile, His/her address, you need all documents for the car+History (If any) this might sound stupid if the car has alloy wheels with a lock secure nut make sure it is in the boot or wherever.