Step 7 - Read the "Buyers Guide" on the Window
Federal law requires every used car on a car dealer's lot to have posted in the window a one page (two sided) "Buyers Guide" that clearly discloses whether the vehicle is being sold "as is" or with a warranty. The car dealer is required to complete both the front and back of the "Buyers Guide", and to give a copy of the completed form to the person buying the car.
Before you purchase a used car, take a look at the "Buyers Guide" in the window of the vehicle. Make sure that you understand the guarantees that come with the vehicle. And, if the dealer makes any promises or guarantees, make sure that you get the promises or guarantees in writing on the "Buyers Guide", the sales contract, or a "we owe" form. If the promises or guarantees are not in writing, and the dealer breaks the promises or guarantees, it can be extremely difficult to enforce.
When buying a used car, you should always try to get the seller to give you some kind of written guarantee, even if it is only good for 30 days.
You can see exactly what the "Buyers Guide" form looks like (both front and back) by clicking here.
Beth Wells
Helping Consumers Get Rid of Lemons, 9 Years Running
You have put a lot of hard work into making sure that your used car is safe and reliable, that your used car has a clean history, that you got the best price possible for your used car, and that you got the best financing for the deal-- so enjoy it. You deserve it! 
Carfax is probably the best known and most trusted of the three. You can get a Carfax vehicle history report online for $39.99. According to Carfax, their vehicle histort reports check for a long list of problems, including: prior accidents, mileage rollbacks or rollovers, multiple owners, structural damage, lease, taxi, or police use, salvage, rebuilt salvage, other vehicle brands, flood damage, total loss history, airbag deployment, hail damage, recall information, service and maintenance history, warranty information, and more. Carfax claims to have the most extensive vehicle history database in North America, with over 6 billion records. And, according to Carfax, they receive data from over 34,000 different sources. Vehicle history reports can be viewed on your computer, tablet, or smart phone, and CarFax also offers a 100% money back guarantee. To request a Carfax vehicle history report, click here.
NMVTIS, or the National Motor Vehicle Title Information System, was developed by the federal govenment. A vehicle history report from NMVTIS will cost you anywhere from $0.25 to $4.95. NMVTIS is operated and managed by the US Department of Justice. According to NMVTIS, their database provides records relating to current and previous state of title data, title issue dates, latest odometer data, theft history (if any), any title brands, salvage history, and total loss history. To request a NMVTIS vehicle history report for just 25 cents, click here. 
only as good as the information that is reported to them. So if an accident or accident repair is unreported, then it will not show up on a vehicle history report. Likewise, if information is inaccurately reported, then that inaccurate information will likely appear on the vehicle history report. 