Being "the car guy" in many of my circles of friends, I get asked to help others shop for a good used car a lot. As a fellow car enthusiast I'm sure you get asked the same questions. As I'm doing this, I figured I'd write it out and maybe help some others out. Here are just some of the guidelines and questions I ask sellers.
First off, do your research. If there's a car you're looking for, find out everything about that generation of the model. Let's use the Nissan 240SX S14 for example. A simple search on Wikipedia will tell you that the S14 generation of the 240SX was made from 1995 to 1998. A 1995 version will generally be cheaper than a 1998 version, but it might also have more mileage and wear on the engine, suspension, interior, and chassis. And every year manufacturers update and fix bugs on a car, so the final years of a generation should have the least amount problems. For some people, though, getting the cheapest version of a chassis is what they're after.
Now that you know what years the car was made, you have to dig a bit deeper than Wikipedia and find out what the differences are between the years. Usually I turn to the specialized enthusiast on a specific forum for that info. This will educate you on the car and help you determine which year or model to go after. For most manufacturers, halfway through a model's generation they will do what's called a "refresh". Here they typically change the bumpers and lights for a cosmetic difference to revive the generation for a few more years. Sometimes it's not a big deal, but in our example of the S14 240SX it is. In 1997 the complete front end and taillights changed. In other cars there might be an even bigger difference, like in engine performance or displacement. Here you'll have to decide which you prefer.
Questions I Ask Sellers:
I just simply don't like salvaged cars. They're like cursed cars, always getting into wrecks over and over.
2. Has the car ever been in an accident? Have any body parts been repainted?
OEM paint is simply the best.
3. How long have you owned the car? Why are you selling the car?
If a seller hasn't owned it for long, I'd be very suspicious.
4. Does anything not work on the car?
It's nice to know that the window switches or door handles don't work before you spend an hour driving out to see a POS.
5. Has any maintenance been done to it lately?
If the car has new tires, a new timing belt, or water pump that's a nice added value.
6. Is there any maintenance that should be done soon?
This will definitely help in negotiating the price. And always re-mention those problems right before you make an offer. It will remind the seller of the flaws.
When you actually go see the car, try to look for overspray on moldings or other common places. This will indicate if it's been repaired from an accident or not; most owners really don't know the history of their cars. Also look at the gap between the body panels. From the factory all panels have a perfect straight alignment with each other. Another thing I'll do is look under the engine and on the parking spot where it's parked to look for oil leaks. If the engine is cold you can remove the oil cap, stick a flashlight into the head, and see if the oil is caked on the internals, indicating they didn't change the oil often. Happy shopping and good luck!