Remember

Before Visiting Any Dealership:
Identify your transportation needs.
Figure out your financial situation and budget. Using the worksheets in this booklet, determine how much you can afford to finance and spend for a vehicle. Remember that a longer-term finance contract may mean smaller monthly payments than a shorter-term finance contract (if all other terms are the same), but you will pay more money over time.
Get and read a copy of your credit report. Errors or accurate negative information can affect your ability to get credit. Generally, you will be able to get a lower rate if you have paid your credit obligations when they are due. You have a right to dispute inaccurate information in the report, and you should do that before you apply for vehicle financing or a lease.
Check auto buying guides, newspaper ads, and other publications and websites to find out the price range and other information for the vehicle you are interested in. Visit dealer websites. Some list their inventory online, by location.
Find out the cost of insurance from your insurer in advance, so you can factor in that amount.
Determine the market value of your current vehicle before you negotiate the purchase of a new vehicle and find out the net outstanding balance on your credit contract. If your vehicle’s value is less than the amount you owe (negative equity), consider paying down the debt.
Compare APRs and financing terms from several sources, such as banks, credit unions, finance companies, and dealerships. Shop for information about current offers online. You may find restrictions on the most attractive rates or terms from any credit source.
Know the difference between buying and leasing a vehicle.
At the Dealership:
Stay within your price range.
Try to negotiate both your purchase price and your finance or lease terms.
Determine whether an offer meets your budget and transportation needs.
Understand the value and cost of any optional products or services offered to you, such as an extended service contract, credit insurance, or guaranteed auto protection. Make sure the payments or other terms quoted do not include these products unless you want them. If you do not want these products, do not sign for them.
Read the entire contract carefully and ask questions about the terms of the contract before you sign. If you are using dealership financing or leasing, ask if the terms are final. Once you sign the contract, you are legally obligated.
After Signing:
Be sure you have a copy of the credit contract or lease agreement, with all signatures and terms filled in, before you leave the dealership. Do not agree to have the papers mailed or provided to you later because the documents may get misplaced or lost.
Know that if you financed the vehicle, the finance source has a lien on the vehicle’s title (and in some cases holds the actual title) until you have paid the contract in full.
Make your payments on time. Late or missed payments can have serious consequences; late fees, repossession, and negative entries on your credit report can make it more difficult to get credit in the future.
If You Experience Financial Problems:
Contact your creditor as soon as you realize you will be late with a payment. Many creditors work with consumers they believe will be able to pay soon, even if slightly late. You may be able to negotiate a delay in your payment or a revised schedule of payments. If you can reach an agreement to change your original contract, get it in writing to avoid questions later.
Know your obligations. If you are late with your vehicle payments or, in some states, if you do not have the required auto insurance, your vehicle could be repossessed. The creditor or assignee may repossess the vehicle in full satisfaction of the credit agreement or may sell the vehicle and apply the proceeds from the sale to the outstanding balance on your credit agreement. If the vehicle is sold for less than what you owe, you may be responsible for the difference.
Know that the law in some states allows the creditor or assignee to repossess your vehicle without going to court.

Source:  https://www.consumer.ftc.gov/articles/0056-understanding-vehicle-financing