Ideally, buy from someone you know & trust.
But you can find a bargain on craigslist.
Look for private parties who have had the car a long time and low miles.
Look for ugly cars with faded paint, cracked windshields & minor issues that bring down the price but not the running condition.
Take a long test drive and if you still like it and want it, have a mechanic check it.
About 18 months ago, I sold my old car on CL. 94 Buick Century. 89k actual miles. Cracked windshield and the AC was broken requiring $250-350 in repairs. I had it 12 years and bought it with low miles and didn't drive a lot. It took me 7 weeks to sell it for $1595 but it was a great car and worth the money.
I was surprised it took so long to sell but I think a lot of people would rather have a prettier car with twice as many miles or something. Silly.
Now, Buick isn't a great car but it is not crap either. A similar low mileage import would cost at least twice as much if you could find one.
In my case, I had put off a newer car long enough and could easily afford to upgrade so I did. And I explained all that in the CL ad. I didn't want to shell out the extra for fixing the AC. But that I would have trusted the car for another 5-6 years easy.