Tell him you can't guarantee that the computer will ship to meet his deadline. That's too damn fast. What if something comes up, and you can't hit the bank for a day?
Tell him that with the number of counterfeit cashier's checks out there, you'll be very careful about verifying it with your bank, etc, and it might not be until the following week that the computer ships out. If he doens't like that, he can pay with PayPal. If he still doesn't like it, he can shove it up his ass.
You're the seller, you get to say what goes.
