there are 2 sides to this. If on ebay for instance the seller lives or dies by his/her ratings. I knew a neighbor that bought a van that was in great condition from someone that sells a lot of used cars on ebay. I would be kind of cautious if they had only one car to sell and had sold nothing else. All car purchases , before the purchase I would review what the seller would do to remedy a defective in your car once it has arrived. If its "send it back" to them that could be costly. If they will pay to have repaired locally by a repair shop you both agree on that would be good. I think there are auto brokers that sell used cars and will inspect a car from someone else before you buy the car online.