The dealers aren’t trying to change the deal after the fact. They are simply asking the customer BEFORE the sale is completed to assume the risk for the government’s default on the $4500 rebate.
If the dealer makes no profit due to the government reneging or just never getting around to meeting their promise, the dealer does not benefit from the sale at all. However, ostammer’s UAW buddies benefit whether the government follows through on the rebate or not because the manufacturer got their money for the vehicle, which then means more cars get built which means more money for UAW workers.
If they’re asking up front then fine. The customer can decide how trustworthy they think the feds are.