That's what's appealing about me entering the racket of flipping undervalued cars -- a few trades might make me thousands of dollars, so I could ideally end on having a really decent ~$14k car mostly paid off.

If it was easy to do why isn't everyone doing it? If you want to make money you really need to be adding value in the process. A car that runs, is clean and has a good record will fetch a decent price every time. There are some pricing errors that occur on Craigslist but they may not be large enough to justify the risk of rushing into a car purchase to beat out the other guy. If you are picking up 200-500 a flip it only takes 1 bad car to eat your entire profit, plus there is a time value of money problem.

You can add value by taking a car that is ugly inside, or doesn't run and fixing it. To get there you need to do good research and take calculated risks. Pick a few models you are interested in and then research parts, common defects and associated costs. You will also need a friend with a truck to help you tow and a place to work. You want cars that people are getting rid of and dont care about getting top dollar for but are still appealing to college students or poor people.

My buddy used to flip bikes in college. Buy dropped bikes in the winter, replace all the panels, repaint and resell them in spring/simmer during peak season. Cars are probably a bit more competitive but there's is a niche there too.