How Not to Buy a Car

Buying your first car? Be sure to arm yourself with research before trotting off to the dealership.

"Confusion is a car dealer's weapon," says Philip Reed, senior consumer-advice editor at Edmunds.com. "The more focused and in control of the numbers you are," the more likely you'll have a positive outcome.

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Here are four common mistakes first-time car buyers make and how to avoid them.

1. Going to the dealership without financing.

One of the trickiest parts of buying a car is the financing, or loan you have to take out in order to pay for the vehicle.

"The 0% financing that's advertised is top-tier financing and might not be available for you," says Mr. Reed. "If you don't have a credit history or much of one, you might not have the credit score required for that level of car loan."

That doesn't mean that you can't get a good rate. Just be prepared to shop around. Compare rates at websites like Bankrate.com.

Find out what you qualify for before going to the dealership, so you have a backup in case you get turned down or can negotiate a better interest rate at the dealership.

Say you get approval for up to $25,000 at 6% from a bank and receive a no-obligation check. You then go into the dealership and see if you can do better.

"If they can beat your rate, you go with them," says Mr. Reed. "If they can't beat it, you know you won't be exploited."

2. Not shopping online.

Many dealerships have an Internet department that doesn't get paid on commission like the salespeople.

The buyer benefits because the worker's job is to get volume out the door, which means you are "less likely to have games played with those guys," says Jeff Ostroff, founder of the website CarBuyingTips.com.

Once you've found an acceptable quote and financing, ask if you can have the car delivered to your home. That way, you can skip going to the dealership in person, where the salesperson has the opportunity to rewrite your contract and sell you expensive extras, says Mr. Reed.

To encourage the dealer to deliver the car, make your offer contingent on free delivery.

3. Paying for extras.

VIN etching, dealer prep, fabric protection—these are all unnecessary extras, each costing at least a couple hundred dollars, that a dealer might try to sell you on before you sign the contract.

The one extra that could potentially be of some value, says Mr. Reed, is an extended warranty if you plan on owning the car for a long time. If you go the warranty route, he suggests calling ahead to negotiate the price before showing up to sign the contract. However, even the warranty isn't completely necessary. "I try to buy a very reliable car and just treat it well," says Mr. Reed.

4. Buying a used car without research.

You can't always tell what's wrong with a used car just by looking at it, so be sure to get a copy of the vehicle history report and to have your mechanic check it out.

"Always double protect yourself before buying," says Mr. Ostroff. In addition to checking out the vehicle history on AutoCheck.com or Carfax.com, he suggests having your mechanic put the car up on a lift to check out everything underneath.

Write to Anna Prior at anna.prior@wsj.com.