It didn't. I worked in the industry as a Sales Manager for many years. I knew exactly what their margin & holdback was. I knew how much Corporate rebate they would get, and I know how sales managers think. I negotiated the the car to the price I was prepared to pay, got it approved by the sales manager and then signed the Offer To Purchase "Subject to payment in full by Amex with no surcharge". I put that in from of him and he said no, so I got up and walked out. I didn't get more than 5 metres from the dest when he agreed.
It depends on the dealer you go to. Family run dealerships are likely to let you walk for this, but large franchises play funny buggers with accounting, and I can guarantee that the surcharge amount would of ended up being charged to the New Car Departments "Cost Of Sale" account as apposed to the individual deal. Dealers will do almost anything to stop you walking away. The GPU on that deal would of remained unaffected.