I wouldn’t buy a car from a private seller over eBay, just because it is impossible to see the car in person. But most of the cars on eBay are being sold by dealers.
I would not have any qualms about buying from a local private seller, as compared to a dealer. When you get down to it, nothing is free. When you buy a “certified” used car from a dealer, you are paying extra for:
A) their inspection of the car, to detect any mechanical abnormalities and impending failures.
B) an extended warranty covering any failures that may occur past the factory warranty period. Often this warranty will exclude certain items that are likely to fail, like window regulators.
If you find a car you like from a private seller, you can just as easily choose to spend the money on A) and B) yourself.
A) will cost around $100, depending on where you take it for the inspection. I would recommend doing this for any used car you buy from a private seller.
B), as a rule, is a ripoff. An extended warranty is an insurance policy. People who sell insurance policies, statistically, make money (otherwise they’ll go out of business). And they make money by selling you policies that cost more than the expected cost of repairs they will pay for.
Additionally, when you buy from a private seller, you may also have the chance to judge for yourself that person’s character, and determine how they may have treated the car. They may even have maintenance records proving that everything was done on time. If you buy a car from a dealer, you have no idea who owned it or what the hell they did to it.
I would definitely not say it’s crazy to buy a car from a private seller. Just get an independent mechanic to evaluate it first.
If you buy a non-certified used car from a dealer (or a used-car lot not affiliated with a specific manufacturer or new-car dealer), you’re really not in much better shape than buying from a private individual. If the transmission fails one month into your ownership, you’re out of luck in both cases.