8 of the biggest scams to avoid when buying a car

"Don't assume because you can configure a car online, that it actually exists," Diaz said. Your dream car, with the exact options and color you want, might not exist on a dealer lot near you.

"If a dealer doesn’t have what somebody wants, they're going to try to sell what they have on the lot,” Diaz said. "They'll put you behind the wheel of a car to test drive it immediately, whether it's what you want or not."

"Before you know it, you're driving out of there with something that's $200 more a month than you wanted."

If you can be flexible about which car you want, you'll be happier in the end, Diaz said. And if you aren’t in a hurry, you might be able to order your dream car from the factory. He noted that ordering a new car can sometimes save you money.

Buying a new car is a big financial decision. It’s also an emotional one.

"People spend a lot of time in their cars," Diaz said. "It becomes emotional because it becomes part of our identity." This works against you in the car dealership, and salespeople know it.

"You forget that you can get up and walk away at any moment," he said.

Less scrupulous car salespeople will "lose" the keys to your trade-in. They'll claim they have to get the car you want from an offsite lot. Or they might be detailing the car they want to show you (Diaz said this could be dealer code for fixing a dent or ding).

The longer you stay at the dealership, the more likely you are to get tired and hungry. You just want to go home.

"If they wear you down enough, you'll say yes to everything," Diaz said. That's when you are susceptible to an upsell you might regret later.

"If you want to make a good financial decision, leave your emotions out of it," Diaz said. "Don’t be afraid to walk away and come back later, no matter how much you like the car."

More Americans are leasing cars these days than ever before, recent surveys have shown.

Beware of a lease that seems too good to be true. When you see a lease advertised on TV with a low monthly payment, it's probably a very low mileage lease with a high down payment, Diaz said.

Read the contract before you get excited about a lease. Go into the transaction with clear knowledge of what you’re getting into.

If you're buying a used car, you need to do more than look under the hood.

Diaz suggested getting a Carfax report to find out about past bodywork or accidents. Find out if the car came from out of state and whether it spent time sitting in water after a flood. Damage that you can't see can be a used car buying nightmare.

Some used car dealers pretend to be private sellers on Craigslist to avoid regulations. Diaz noted that you can't complain about problems with these purchases because the dealers are usually fly-by-night operations that will disappear quickly.

His pro tip for used car buying: "If you're going to buy a used car, try and buy it from a dealer that sells that same brand new." In other words, don't buy a used Toyota from a Honda dealership.

"If there's warranty issues, you'll be able to resolve them better," he said.

Diaz said that most people walk into a dealership and show all their cards up front. When you hand over the keys to the car you want to trade in and name the car you want to buy, you've given the dealer leverage that can be used against you.

Diaz suggests that you leave your trade-in vehicle out of the equation to preserve your leverage.

Individuals also run used car-buying scams.

"Beware of something that sounds too good to be true," Diaz said.

He noted that someone might advertise a car online for much less than its value, with a heartbreaking story about why they need to sell it quickly. Then you find out that the car is out of state. And you need to wire the person the money.

Don't wire the person the money. If the deal seems to be too good to be true, it is probably a scam.