> i can't imagine why you'd carry cash for such transactions and not a cashier's check.

because people forge cashier's checks far more easily than they forge cash. I certainly wouldn't take one as payment for a truck without going to the issuing bank first and withdrawing the money (as cash). In which case, there is no need for the check.

For smaller purchases, sure. For large purchases, I refuse to do business with anyone who insists I show up with thousands in cash. Even taking civil forfeiture out of the equation entirely, there's just too much that can go wrong.