est APR means the estimated annual percentage rate you will pay for a loan. This is the interest rate you will be charged per year on the money you borrow. The term (estimated) means that the amount of interest is either variable, or that they quote different interest rates to different people for the same car loan, depending on their credit score and how much you negotiate the terms of the loan.
When a car dealer takes a loan application and gets you financing, they typically mark the interest rate up a certain amount (usually 2 or 3 percent); this additional money goes into the dealer's bank account every month when you make your loan payment to the bank. If you are a good negotiator, you can sometimes get the delaer to sell you the loan at cost (they make no money on the loan, which means you get a lower interest rate and a lower monthly payment).
In general, you will usually get the best interest rate on a car loan if you go to your own bank and arrange your own car loan. The only exception is if the manufacturer is offering special loan rates that are below market price (like zero percent during a clearance sale).
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