We recently bought a new car. Multiple dealerships told us we could not get a better deal paying cash. The opposite is actually true. You can get a better deal by financing. Crazy.
A good friend of mine owned the Motorcycle BMW dealership in GSO and Durham before he passed away. We met as a result of one of my best friends having bought several new bikes from him in the past, and then me buying a new bike from him in 2005. When I bought MY bike he told me whatever I do, NOT to finance it thru the dealership. To get my own financing or pay cash, whatever, but at a dealership, the GOAL is to get you a great rate (let's say 5%) but present it to you as 6.2%. That way the dealership gets that 1.2% kickback from YOUR payment, every month.
Haven't bought a vehicle from a dealer in 10+ yrs, so I have no idea how the process works anymore. Do you still haggle?

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We just bought my wife a new (ish) car.
New vehicles mean nothing to me and I don't care for all the new doodads and whatnot, but this isn't me. My vehicles are 18 and 23 yrs old and I'm happy as a clam with them.
This is me also. MY newest vehicle is 2011 but this is HER.
I have heard people say they do they financing to get whatever promotional deal is being offered, and then just turn around and pay off the loan asap. But if you plan to do this, check whether there is any penalty for early payment.
This is what we did. There was little haggling on the OTD price. But when financing was offered, there were HUGE incentives that changed the bottom dollar. Because it would take 2-3 days to get the cash needed for this purchase, as well as the BIG difference in bottom dollar because of the incentives to finance, we decided to go financed thru lexus and got 4.9% for 36 months. The plan was to pay it off the next day. (this is where it's VERY important to be sure there is no penalty) but you can't really do that. You basically have to wait till the coupon book arrives and you get a 10 day payoff. So we DID end up paying a few $100 in interest, but it was still a MUCH better deal than if we plopped down cash for the car. Whole process took less than 2 hrs from test drive to leaving the dealership.
The car before THAT I DID walk into the dealership with cash (well...they took a personal check) and the process took nearly 3 hours for some reason

(to be honest, we did sit and argue about dumbass fees, tacked on crap, and protection I never asked for. Damnit if the price is $200, I'm not leaving there $400 poorer

THIS is what you have to really watch.They lure you in with a sale price, but all that goes out the window when they put the deal on paper and start adding stuff up.) I was FUMING when I left there. There's no sense in that. And I truly got the feeling they were just as upset that I paid cash (see first quote for reason I believe that)and I ONLY paid for the car...not paint protection, warranty, docking fee, tuesday fee, lot shipping surcharge, coffee fee...etc