I have done it quite a few times in the last 2 years. Out of maybe 15 cars I lost money on 2. Usually around $500 profit. I started detailing, though, and if I can make decent money with it I won't bother flipping cars anymore. It's a LOT of hassle, for little profit. You have to get the car somehow, clean it, hide all the defects, and always talk yourself through the sale...if you tell someone straight up you do this on the side they are usually not too interested anymore. It does feel good, though when you do make a couple of bucks
It's definitely doable, though.