We actually did what u/2ReddYet is suggesting. Back in 2016, we had negotiated online to get the car I wanted. (They had to get it shipped from Japan because the exact configuration I wanted wasn't available in the US. And I wasn't in a hurry.)

WE get to the dealership...and there's a snafu. Apparently I hadn't told them I was expecting to write a check for the car (my first time!) So. I debated with myself and my wife for a minute or two, and then I asked two questions:

1. What's the minimum I have to finance to qualify for the incentive?
2. how soon can I pay off the loan and still qualify for the incentive?

I ended up financing about 1/3 of the price of the car (the minimum), and as soon as the first bill came in, I swooped in and paid off the loan in full. I paid $22 in interest to get that $500 financing incentive.

BUT... 2016 was a different market....and we bought new.

Oh man, so I just went through the hassle of buying a car in November. Two weeks looking for the car I wanted and going into dealerships to "negotiate." It was a pretty bad experience.

I was looking at a Kia Telluride, and the dealership put a $5k market adjustment just two lines below the $5k savings. The answer we got was "thats just how it is." We reminded him that he told us he would waive the $5k we came in today, and he said he couldn't honor it. Waste of 2 hours as they treat you like a dummy the whole time. I also had another dealership raise the price $2,000 and drop it $2,000 making it look like a deal.