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Here you go: http://siy.cars.com/pdf/carscom_bill_of_sale.pdf
This can be just written on a word document. Something like this:
I, (buyer), purchase the following vehicles from (seller) for consideration of (purchase price) paid via (check, cash, etc.):
The (seller) agrees to transfer full title and ownership of the above vehicles to (buyer).
They do not have to be notarized but you can definitely get it notarized if you go to the notary with the seller. This will prove that the signature is that of the seller if he disputes it in the future, especially if you're worried that this will be a scam.