No doubt about it, if you're purchasing a used car you need to learn how to read a CarFax (CF) Report. Many used car dealers run a CarFax and make it available, for free, on many of their used cars for sale. Every car made since 1981 has the 17 character VIN (Vehicle Identification Number) stamped on many components of the car's body.
If the used car you are interested in doesn't have a CarFax already run you MUST run one yourself. Do NOT, under any conditions, buy a used car without viewing the CF about that car. It costs a few dollars and can save you a small fortune in return.
You have no say in the matter when your car is involved in a collision and the body shop reports the damage to CarFax. When an automobile fails the state emission inspection, that fact is reported to CarFax. When an automobile is destroyed by a flood, hurricane, or other types of water damage that fact is reported to CF.
There are squads of criminals that buy totaled and water damaged cars and them up; you would not know that they were totaled. Well, until about six months later when the entire automobile rusts to a hulk one night. Cars, totaled in horrible auto accidents, can be fixed up and look like nothing ever happened until all four tires wear out in two months.
The indicated number of owners, and type of owners, can keep you from purchasing a heavily used corporate/municipal vehicle that was bought, for a few bucks, and repaired to look like it was driven by a little old lady. If the odometer has been fiddled with odometer warnings point out this fact. A Geek, with a PC, can easily roll back the electronic odometer setting.
CarFax checks on all the crazy legal things that can occur to a car title. CarFax catches all kinds of scams, run by crooks, that can impact the car title. There are salvage, junk, rebuilt, fire, flood, hail, lemon, mechanical limit types of titles and CarFax alerts you to anything but a normal title.
Pay for a CF if there are no problems with your used automobile for sale and make copies and hand to folks who drop in to look at the car. Tell them that CarFax will buyback the car if they find something that CF missed - they have that guarantee on every car that passes all their checks.