There is no guarantee that you’ll get the best rate, even if you have great credit. In fact, I know you’ll never get it unless the manufacturer offers an incentivized rate, such as 0.9% for 60 months.
The best rate for non-incentivized loans of course is the “buy rate”. That’s what a lender says it wants as an APR. NO ONE gets the buy rate. Dealers can mark it up and they all do. Some states have a cap on how much over the buy rate the dealer can charge. For instance, if the state you live in has a 3% cap and the lender tells the dealer it will fund the loan at 5.5%, the dealer can then tell you that you qualify for an 8.5% APR. The difference goes to the dealer.
This 3% cap gives the dealer some negotiating leverage when it comes to your monthly payment. He can “sweeten the deal” to get you to sign. But no matter how much he knocks off the interest rate, you’ll still be paying above the buy rate.
So what can you do? Demand an “option contract”. That gives you 5 working days (or longer depending on the dealer) to find a lender on your own who can beat their deal. If you do, they shred the contract. If you don’t, the contract goes through. If any dealer refuses to give you an option contract, walk out! They may have something to hide and you’ll want no part of a shady dealership.
And remember what I said about walking out.