In over 90% cases, people tend to sell their cars only when that needs repairing (or temporarily repaired) or develops problems. Therefore on the supply side, you are forced to buy such cars and sell on, the same to the buyers who have to spend more and more money to fix them right. The buyers, after sale, therefore would always remain unhappy with you. The profit margin may range between 7% to 10% on each deal, while in most problem cars you would face loss situations, which is why many take exit from this business early.