A few years ago, you could definitely make a fair amount of scratch just bouncing gear between Craigslist and eBay, but nowadays, stuff just isn't selling like it used to.
I'm sure if you're willing to do the legwork and a little haggling, you could get get something going. However, right now, people just don't have as much spendy cash to go around.
edit: I don't want to discourage you or anything, but I also don't want you to end up with a bunch of $350 guitars that you can't sell for $250, which is where a lot of folks are finding themselves nowadays.