My youtube feed suddenly got a former(?) sales guy and his son (grandson?) talking about car buying. I don't watch much of it but I did click on a few of them... so win for them.
They mentioned, if financing through the dealer, to ask what the buy rate is. The dealer is going to get an APR from the banks they work with, but they can then raise the APR and pass that along to you. Adding 0.25% so you don't have to deal with the bank may be worth it to you, but they could be adding 1% or even 2% on top of a 5% APR, and now I suspect you are talking about real money going into the dealers hands. Money that, like all other aspects of the deal, should be negotiated.