Getting a higher rate directly from the bank does not necessarily mean that the dealer is not making any money on your loan. It is likely that the bank just offers better rates through their dealer partners because: 1. it's less hassle than dealing with retail customers, and 2. the dealer market for loans is more competitive.
I mean yes, I'm sure they're getting something, but the margins are so thin I don't think it's even worth considering. Consider a $50k car, dealer offers you 1% via bank. At best the bank is only taking half of that (0.5% is already ridiculous for a not-really-secured loan, considering new car depreciation), so over a 5yr loan the dealership makes... $1250. That's, what, one week of salary for one of their salesmen? I just don't think it's as much of a factor as we think it is. People talk about the dealerships handing out $10k discounts because "they make their money on financing" but the math just doesn't support that unless you're doing credit-card-interest-level loans.
Usually people cite the financing incentives when people mistakenly use the "cash is king" strategy when trying to negotiate on a car, but it isn't the only way they're making money. Dealers make significant money from manufacturer kick-backs and service too.
Also 1% sounds too low for an independent bank loan, even with the now-cratered loan rates. I am guessing that is probably a subsidized loan through a manufacturer's bank. Manufacturers have long offered artificially low rates through their own banks to help move product.
