You will have to forget about your regular successful image and to play a guy who only deals in cash. ( i. e. for some reason you don't have credit cards). Just say that you only have X much money on you. These people love cash, they will understand. When you reach consensus, just say that you have to go to the car to get your X+whatever (if anything) cash and run to the bank.
That way you'll make it much easier for him (and for yourself).
Works for me everytime.