I've flipped a lot of guitars - for a decent profit? Usually not.. but I do it because I love working on them, not for the $.
Usually I will find a cheapie or a salvageable basketcase and fix it up, new finish, etc. Things that add curb appeal. But you need to know a fair amount to assess the condition of a guitar before you snag it - some things may not seem like a big deal in the shop, but once you get it home and do a careful assessment of the needed repairs, you may end up with more work than you bargained for.
Also, the used guitar market right now is oversupplied - there are guitars I now "know" on CL because they've been posted so many times, usually with a desperate price slash. Some have been going on over a year unsold.. If the economy is bad, people tend to sell recreational items first, which for most is the guitars. End result, it's a buyers market, but once you get a hot deal, unloading it is going to be a challenge, unless you have a reliable place that gives decent prices on used gear. Such as the music only pawn shop in my town. But even then, they have a profit margin to meet too, so it's a last resort.
Custom parts guitars could be another way to go, but again, think in terms of branding - I'm not the least bit interested in the standard Strat from Warmoth/GFS/etc. parts, since I can do that myself and it's been done a million times before. But if you do something unique and different than everybody else with those parts, you can stand out from the pack and start defining your 'style'. Things like your own design of headstock, wild paint combos, wiring configurations.. and besides, typically you won't get back out what you put into a parts guitar unless you really make it something special.
My advice to you would be to start with set-up type things around campus, post flyers out in the student union, give decent deals on your work (like $10 for a basic string change, $40 for an action setup, $60 labor for pickups) and get your name out there! Networking is key with such things.. consider every guitar you work on as your business card that the owner will carry with them. Become the "Guitar Guy" on campus. If you do good work, treat your customers right, and love doing it, eventually people will seek you out.