If you're buying specifically to flip, I'd rarely pay much more than scrap value. Can't really go wrong there. Make sure all the safety stuff works (lights, signals, brakes, etc.) Even if they're the cheapest damned things you can find, a NEW set of tires will set your car apart from others in that price range. Average Joe doesn't want to have to sink another $500 into a car he just paid $2,000 for.
When advertising, never mention "negatives" unless they're a safety issue or the car is in poor running condition. In the interest of being honest, I used to do the "Good" and "Bad" thing. Dumb idea. It's the buyer's responsibility to ask questions regarding maintenance, look under the car for rust, etc. If the goal is to SELL THE CAR, highlight the positives. Take GOOD hi-res photos, and get the buyer thinking about how nice it is before they ever see it in person.
Personally, I take the "Soft sell" approach once someone actually comes to look at the car. After all, I'm not doing this for a living. I don't try to sell them the car. I just answer questions.
Have a sense of humor. Inevitably, someone will say "Well, KBB says it's worth 'x'." To which I'll say with a smile, "That's great! Hey, when's the last time KBB bought a car from you?"
My philosophy is DEFINITELY different when selling here or to other enthusiasts, but to strangers on craigslist? Buyer beware.
If you don't mind wrenching a little, a great strategy is to buy cars that have a typical mode of failure once that part has failed. A friend of a friend buys nothing but dodge caravans with dead transmissions, replaces the transmission, then sells it for no less than $1k more than what he's got into it in parts and labor. Do that once a month and you've got an extra $12k a year free and clear in your pocket - or to max out your retirement fund with.
Build a man a fire, and he'll stay warm for a day. Set a man on fire, and he'll stay warm for the rest of his life.
