I made some pretty good money flipping cars last year and then I lost my *** on some too.
Craigslist is the best place to buy cars. Buy them low and sell them high just like the stock market. You can even find cars on Craigslist cheaper than at the auctions, unless you have a dealers license. If you buy from an auction, you have to pay vehicle title/registration & sales tax. If you buy and resell privately, you can avoid those extra fees.
The problem with flipping cars is, like any business, the learning curve. You have to know what cars resell well, what to look for mechanically, what cars to avoid, etc. It helps if you stick to a couple types of cars that resell well and become an expert on them and their value.
I went through the school of hard knocks trying to learn this business and here is some of the best advice I can give you.
If you're not mechanically inclined or if you don't have a reliable and inexpensive mechanic, avoid cars that need repair...parts & labor costs can kill your profit quickly.
People would rather buy a car that looks great and runs like crap, rather than a car that had cosmetic issues and was mechanically perfect.
Your local junk yard will save you a ton of money if you don't mind getting your hands dirty.
Your Totota, Honda, Hyundai, Lexus, Acura are quick sellers but used parts can sometimes be hard to find since they are in such demand.
Forget what the car price guides tell you. NADA or KBB might tell you a used car is worth 5K but if you list it at that price, you may never get a phone call. The best way to determine value is by compare the vehicle to similar vehicles on Craigslist.