The best way to do well is to pay way less money than you eventually sell the vehicle for. Easy to say, not so hard to do and definitely worthy of a little fine tuning, a la good research. I learned how to do good research when I was in school to do my Master's. I apply the principles I used to succeed in grad school to be successful in my research. Without getting overly technical and belaboring the issue, common sense and study prevail. To be fair, I also employ techniques I learned in Elementary School such as making an outline with paper and pen before writing. I find that the outline helps to reinforce my thought process as I type on the computer.
Well, I got a little off topic there, but back on track now. Maximizing your profits by buying at low cost auctions is how actual licensed car dealers make a tidy profit and you can do it yourself on a smaller scale with a little initiative.
If you're still reading, I recommend government auctions because they generally have low mileage vehicles with intact warranties. A lot of what ends up there is from repossessions, but that's not a bad thing. All it means is that the person who bought the car did not make payments for a certain amount of time and that the bank then hired someone to bring it back to them.
Rather than pay exorbitant storage fees (imagine if you were a bank and had to store fifty repossessed cars), the bank will let the cars go to auction for whatever they can get and cut their losses. You pay way less than even private sales, which ups your profit margin. How do you find out where and when these auctions are? You can check out Gov-auctions.org for more information. Good luck and happy car hunting!