Some forms are intelligent enough to recognise "made up false" account numbers and tell you that this is not a valid account for the bank identifier code you entered.
Nahhhh - 've never seen a halfway decent attempt from anyone, nothing you'd remotely consider "serious" or "professional". The very poor attempts don't even work (usually for obvious reasons), the slightly better ones are so obviously amateurish that really nobody could fall for them. Only those deserving so anyway... :rtfm: