buying cheap used gear and trying to resale cheap used gear is not going to be a particularly successful venture.
Ah, but that depends on the definition of "successful." The OP hasn't set the bar very high, just the occasional $50-$100 profit. In a big enough college town with a music scene, that's doable. However, a good candidate to "flip" may only show up once every one or two months, and someone else may get to it before you do.
Fwiw, I have started doing this. I don't expect to make very much money to speak of, but it is possible to turn a small profit. (As an example, a year or 2 ago I snapped up, not to flip but for myself, an Epi T-bird bass for $100, and I know I could've resold it for $200 or at the least $150, had I not wanted to hold onto it.)
However, it may take a good month or two to move something, once acquired. I look on it like this: I get an axe that's new to me, and available to play, for a month or two, and when I resell, at a minimum I have yet to lose any money. So it's like getting paid to have an extra axe laying about.