You don't need us to tell you that buying a used car can be a stressful experience.

But there's one way to alleviate some of the fear that you'll drive off in a dud: You could opt for a certified pre-owned vehicle. All certified vehicles are inspected by a manufacturer-trained mechanic and come with extended warranties that are backed by the manufacturer. Many programs even throw in extra services that once were offered only with new vehicles. Lexus, for example, provides free roadside assistance and a free loaner car if yours is in the shop.

Not all programs are failsafe, however. While some warranties extend for several years, others last just a few months. And there's always the chance some unscrupulous dealer will try to pass off any old car as an officially certified vehicle.

Here's how to get a good deal.

Delve Into the Details
Some certified pre-owned programs are much more comprehensive than others. Ford, for example, offers a 6-year or 75,000-mile warranty and roadside assistance, whereas Buick's warranty covers just 3 months or 3,000 miles and offers no roadside assistance, according to CarsDirect.com. For a complete listing of programs, see Edmunds.com.

Prepare to Pay for Peace of Mind
Considering all the perks and assurances that come along with a certified pre-owned vehicle, it makes sense that these cars are more expensive than ones that come without a manufacturer's stamp of approval.

How much more can you expect to pay? That will vary by make and model, but the difference tends to increase with luxury cars, says Jack Nerad, editorial director Kelley Blue Book. According to figures from auto Website Edmunds.com, you could expect to pay an average of $22,461 for a certified 2003 Ford Explorer Eddie Bauer four-wheel drive SUV. (The original MSRP in 2003 was $34,635.) If you bought that same truck, uncertified, from a dealership, it would cost an average of $19,316. An individual would charge an average of $16,950.

Watch Out for Dealer Certified Vehicles
There are 2 types of certified pre-owned vehicles: ones that are backed by the manufacturer and ones that are certified by someone else. Watch out for dealerships and independent used car lots that simply slap a "certified" sticker onto a windshield and then try to pass that vehicle off as having gone through the same checks as dictated by a manufacturer's program. Dealer-certified cars tend to have less-stringent inspection policies and shorter extended warranties than manufacturer-certified vehicles, says Steve Nolan, spokesman for Cars.com.

How can you tell the difference? First, only a branded dealership can sell its own manufacturer-certified vehicles. So if a BMW dealer is trying to sell you a Mercedes, or if you're shopping at an independent lot, you can be confident that the vehicle in question is dealer-certified. It's also a good idea to ask to see all the paperwork that guarantees the car is backed up by the manufacturer, says Karl Brauer, automotive expert with Edmunds.com.

Go Online
Even with certified vehicles, you need to make sure you're getting what's advertised. "We've found that some dealerships are willing to certify cars that wouldn't meet another dealership's criteria," says Kelley Blue Book's Nerad. Fact is, even though all dealerships must make sure that their certified inventory passes the same 100+ point inspection process, there's some wiggle room that's left to the mechanic's judgment. So while one mechanic might think it's fine to certify a car that has been in a small collision but is otherwise running well, another might not, says Nerad. To protect yourself, make sure you ask for a full maintenance history and inspection report, and run a vehicle history report from CarFax or AutoCheck.

Learn about buying a used car.

Best Certified Pre-Owned Programs
Brand	Warranty	Roadside Assistance
Dodge	8 year/80k miles*	Yes
Jeep	8 year/80k miles*	Yes
Acura	7 year/100k miles*	Yes
Honda	7 year/100k miles*	Yes
Nissan	6 year/100k miles	Yes