A cashiers check from the bank itself (as the payer) would be safe. A cashiers check from a private party can be cancelled by the private party prior to being deposited into an account. I have sold a lot of cars and will only accept a cashiers check if the buyer is patient enough to wait for me to send them the title once the check clears. They get the car and a bill of sale while we wait for the check to clear. Wire transfer is the safest option.