Before you buy, research the price of the car. Sort through Ebay and Craigslist until you figure out the average price that the vehicle is selling for. If you're expected to pay the average price well then it's a pointless buy. If the car is for sale for well below average then be suspicious as to the reason. The car could have a major fault that's difficult to detect. For example, a friend bought a cheap Volvo a few years ago and then found out that the car was perfect up until about 45 minutes running time when all of a sudden in traffic the auto transmission would select all the wrong gears. In those cars (and many these days) the gearboxes are sealed so he had to choose to replace the gearbox, a costly mistake.
Anyway, just be careful on a cheap purchase but also it may be genuine. An elderly owner who can't drive any longer, a person who desperately needs the cash. So if you hit a home run with a genuinely cheap car then if you've done your resale research, you'll know what price to sell it for.