I mostly buy crown Victoria police interceptors. Why? They are reliable, there's a huge following for these cars, and they're cheap. I know the ins and outs of these cars. For example, these cars have 8 coil packs. Each one fires one spark plug. A simple design but they are prone to break. They are also $50 a piece at your local parts store. When the engine misfire code pops up, 99% of the time it's a coil pack. A lot of people will sell a car cheap if its running badly and has a check engine light on.
As long as you stick with a certain car, you'll make money. You'll also have extra parts laying around for the next car you decide to buy. Keeps repair costs down and your profits up. If you have any questions on which car to buy just send a comment below. Ill respond in a timely manner. Thank you